Grandpa is good-natured, cheery, and funny. He may not always have the best piece of advice for Arnold but his heart is always in the right place. While not quite to the same extent as his wife, he has a rather eccentric personality similar to both his father and his grandfather. Though he's generally happy and good-natured, he can get rather grumpy when dealing with the antics of his wife, Arnold's friends, and especially the boarders.
Grandpa is notable for his many odd protrusions, such as a pronounced Adam's apple, bony elbows and knees, pointy cleft chin, and what appears to be some kind of lump on his head. He has a long, pointy nose, and is completely bald (with the technical exception of his gray eyebrows). He wears a light gray T-shirt, brown trousers with red suspenders, and light brown shoes.
In Hey Arnold! The Movie, "April Fool's Day", and "The Journal", his Adam's apple is strangely absent, and his head appears more thin and tall.
In Hey Arnold! The Jungle Movie, Grandpa now wears a different white shirt, the same brown pants but with a belt instead of suspenders, and a sweater. His chin was also redesigned to make it look a little less phallic.
BiographySunset Arms boarding house, assuming he can get the boarders to pay the rent, which is no guarantee when you remember that, with the possible exception of Mr. Smith, none of these people apparently make enough money to be able to live anywhere where they have their own bathroom. In accordance with the unwritten "everybody in the boarding house has to have some sort of musical talent" policy, Grandpa plays the drums (in the movie, at Blockapalooza).
Although he gives often poor advice and is rather goofy, Phil is a very great grandfather and wishes ill-will to anyone who doesn't love Arnold. He calls Arnold by the nickname "Short Man".
Phil has accomplished many things during his lifetime. In "Veterans Day", it was revealed that he was a private in World War II, and through a strange chain of events, took out a company of German troops and made way for the American forces going to the Battle of the Bulge, and was, according to him, the person who beat up Adolf Hitler or Joseph Goebbels. He was also a champion Chinese checkers player and tied for first place with his long time checkers rival in the last city tournament (which gave him his nickname "Steely" Phil). In "Haunted Train" he stated that he worked for the Great Northern railway. He and Jimmy Kafka also apparently worked on the construction of the Grand Coulee Dam.
Throughout the series, Grandpa has come across many people who have been considered his rival, including the rich Rex Smythe-Higgins, Robbie Fisher, and his childhood friend Jimmy Kafka. He also occasionally has a rivalry with Big Bob Pataki in a few episodes. Grandpa also is in peak physical condition for his age and can bench over 210 according to Gerald, and he can also do a one-hand push-up. In many episodes, Phil goes out of his way in order to please Arnold but knows that he can never replace Arnold's parents. In the episode "Helga's Locket", he even took an awkward affection to Helga's infamous locket of Arnold ("Helga's Locket"). However, Phil loves to prank people and never passes up a chance for a good laugh at his grandson's expense.
In the episode "Girl Trouble", it is revealed that he and Grandma were in the same class as children during the Great Depression (there were no jobs back then). She had a huge crush on Phil, but could only express it by picking on him, very similar to how Helga does with Arnold in the present. However, Phil eventually had no choice but to drop out in order to aid his family during the Depression, and never graduated from elementary school. Regardless, the two eventually got together. In the episode "Back to School", he attended Arnold's school and successfully completed the sixth grade.
In the episode "Grandpa's Birthday", Phil claims that every man in his and Arnold's family is cursed to die at 81, which he will be in several days. Though he goes about life as if he's going to die, he does not die when he turns 81, when Arnold figures out that the family curse is 91, not 81. So, presumably, he will have 10 more years to live. His doctor however after prompting from Arnold to get a checkup tells him that not only is he the healthiest 80-year old that he has ever seen, stating that he has the strength of an ox, but he could theoretically live to be 150. Assuming that the events of this episode take place in 1998 (the year it was produced), then Phil's birth year (along with Gertie's and Mitzi's) can be pinpointed to be 1917.
Grandpa drives an old green Packard that he has apparently owned since it was new. The Packard is Grandpa's daily driver, and he is very attached to it, calling it his "one true love" in "Grandpa's Packard". It is also shown that the Packard's radio is stuck on Hillwood's local jazz radio station. Grandpa took Arnold and Gerald on a camping trip in the Packard in "Roughin' It", and Grandma once took it (more than likely without Phil's knowledge) when she and Arnold went to rescue Lockjaw from the aquarium in "Field Trip", despite her apparent lack of a driver's license. The Packard was involved in a minor fender bender with Big Bob Pataki's car in "Grudge Match" and Grandpa inadvertently drove it into a large hole a few times in "Mr. Green Runs". After accidentally running the Jolly Olly Man off the road when not paying attention to his driving, the unstable ice cream vendor disguised himself as an attractive older woman and tricked Grandpa into giving him his address, then stole the car during the night. He actually repainted the Packard red and drove it around for a couple of days until Grandma and Arnold tracked him down. Grandpa decided not to press charges if the Jolly Olly Man repainted the car green. The car was returned to its original color and was last seen driving over a bridge with Arnold and his Grandparents inside.
- "Never eat raspberries."
- "Where's the siren? WHOO WHOO WHOO!"
- "Your Grandma made raspberry cobbler."
- "How about you help yourself to some WORMS AND COCKROACHES!!!"
- In the episode "The Flood", Grandpa states that he remembers the "Great Flood of 1916", though him remembering it would be impossible because he was born in 1917, a year after the flood. This can be attributed to him misremembering or making up the story.
- The Hey Arnold! series seems to take place in the mid-late 1990s, and there are several modern inconsistencies with Phil's Packard. Even though the car is more than 50 years old in the series, it is Grandpa's only vehicle and the one he drives regularly. The car is shown to have modern seatbelts in many episodes. Even though Packard was the first car company to introduce an automotive air-conditioning system, in 1939, Grandpa's Packard does not seem to have it. Despite this, the whole boarding house family is seen driving down to the beach with the windows up in "Summer Love". It must have been pretty toasty in that car. The Packard is shown to have its original radio, and considering the car's age, it is probably an AM radio. However, it is able to pick up some local FM stations in Hillwood City, like M-Jazz.
- Phil and his wife Gertrude (Pookie) had a similar relationship to Arnold and Helga's with each other when they were kids. However, Gertie's pranks were often meaner, more old-fashioned, and more malicious than Helga's are to Arnold. This relationship was possibly meant to foreshadow Arnold and Helga getting together.
- In "Part Time Friends", Phil informs Arnold that he should redeem his friendship with Gerald before they waste their whole life not speaking. During a dream that night, Arnold imagines himself as an old man boarding the bus only to find Gerald sitting; the two begin to bicker. At the end of the sequence, a zombie version of Phil with green skin and a double toned voice appears in the back of the bus to deliver a cryptic message to Arnold before having his jaw fall to the bus floor. This scene is commonly considered one of the more frightening moments of Hey Arnold by most fans.
- In "Back To School", Phil hints that he might have been part of the 60's hippie era. When he tells Arnold that he is too old and doesn't have enough brain cells to go back to elementary school, Arnold replies that he "is not that old and still has plenty of brain cells" to which Phil replies: "Not since Woodstock". It is very likely that he is referencing the massive LSD use in that festival. However, considering his birth date being 1917, he would have already been 51-52 in 1969, the year the festival was carried, which would have made him too old for a hippie, who were typically young. It might be possible Grandpa was going through a mid-life crisis at the time.
- His voice actor, Dan Castellaneta, also voices Homer Simpson, Mayor Quimby, Abraham Simpson, and several other characters on The Simpsons, which was created by Matt Groening, Craig Bartlett's brother-in-law.
- Castellaneta's voice for Phil was noticeably different during the early episodes of the series.
- Phil appears to have a crush on celebrity Hedy Lamarr as shown in "Big Caesar" when he gives a picture to a reporter who says it is an autographed picture of Hedy Lamarr and again in the same episode when he asks why he couldn't marry Hedy Lamarr; in "Veterans Day" where he is shown with the same picture and lamenting on how he wishes to marry her; and in "Helga's Locket" where he asks Arnold that instead of putting a picture of Pookie in a heart-shaped locket that he put a picture of Hedy Lamarr.
- Throughout the series, Phil has been shown to exaggerate stories, especially about his own past. The most notable one being the one where he beat up Adolf Hitler.
- Similar to the running gag where Arnold's last name isn't revealed, Phil is sometimes referred to by his nickname "Steely Phil" instead of his full name.