- Coming, Helga.
Phoebe is very sensitive, shy and fragile and usually gets emotional when something bad has happened to her or someone else. This makes Helga often take advantage of Phoebe and treat her like a slave, rarely thanking her. Whenever Helga yells at her or insults her (sometimes for no reason), Phoebe fearfully apologizes, even if she never did anything wrong. She is one of the most intelligent children out of Arnold's friends. An example of Phoebe's insecurity is that she always tries to be the first one with the answer, and isn't exactly thrilled when someone else does better ("Ms. Perfect", "Phoebe Cheats") Also Phoebe is also kind of a Pushover ("Phoebe Skips").
Phoebe has a huge bun of black hair at the top of her head bound by a small yellow scrunchie and wears large cat-eye glasses with blue monochromatic lenses, a blue sweater that is too long for her (which covers what she's wearing for a bottom) and matching shoes. Phoebe's of short stature and has a squeaky voice (though it was less squeaky in the earlier episodes).
In The Jungle Movie, she wears a white shirt with a blue-collar, a blue jacket, a light blue skirt, and green shoes. Her hair is now noticeably longer, and the bun has become a short ponytail.
Phoebe was born in Kentucky and, at some point, moved to Hillwood at a young age. She has a sweet, likable personality with a high intellect. She is one of the nicest characters in the franchise and is said to be Helga's only friend.
Among her most notable moments was when she won the City Academic Bowl ("Phoebe Takes the Fall"), a competition that she shouldn't even have been in, as Helga, in an attempt to win the only trophy her older sister Olga never won, had won her school's spot at the Bowl by forcing Phoebe to miss the final question (ironically, McAfee did not receive credit for the role in that episode). At the opposite end of the spectrum, she was utterly humiliated in front of the entire student body ("Phoebe's Little Problem") when she was caught passing gas into a microphone on stage as she was receiving an award, and subsequently refused to ever go to school again (somewhat ironically, the award was for her perfect attendance). Among her other achievements are winning the Parents Tournament Weekend with her parents ("Parents Day") and the City Go-Kart Grand Prix with Helga and Harold ("Grand Prix").
She's also pretty good at handling a fencing sword ("Phoebe Cheats"), even when it's a flashlight ("Wheezin' Ed"). There is some evidence that she is musically inclined as well; she's carrying what appears to be a string bass in "Helga on the Couch" and is practicing some sort of large horn in "School Dance". (However, music is one of those disciplines where you need creativity, and that seems to be one of few things that Phoebe lacks, if "Phoebe Cheats" is anything to go by.) Just as Gerald hangs around with Arnold, Phoebe hangs around with Helga, who considers Phoebe her best friend (she even says so in "Magic Show", after yelling at her), mainly because Phoebe is probably the only person who likes Helga the way she is ("Helga's Makeover").
Phoebe is Helga's shoulder to cry on, down to the point where seeing Helga cry makes her cry as well. It's also shown that Phoebe has a crush on Gerald.
Crush on Gerald
Main article: Phoebe and Gerald
Friendship with Helga Pataki
Helga often makes Phoebe her own personal assistant and hardly ever thanks her for anything, no matter what she does. Another reason is that Phoebe is deeply afraid of Helga and can’t stand up to her since she's shy and Helga is mean to her all the time. Still, Phoebe is around whenever Helga needs someone to talk to. She’s also one of the few people who knows that Helga is in love with Arnold, (the others being Lila, Brainy and Dr. Bliss) and sometimes helps her keep her secret safe ("Helga Blabs It All", “Helga Sleepwalks” and "Helga's Parrot"). While it's never shown exactly when Phoebe figured out how Helga really feels about Arnold (though it's sometime around Season 4, before "Helga Sleepwalks"), she's also smart enough that she wouldn't let anybody know that. Phoebe seems to be the only person Helga trusts, mainly because Phoebe is the only member of the gang who actually likes Helga.
There seems to be some question as to how her last name is spelled; her school record says "Hyerdahl", but the credits to "Phoebe Cheats" and the award she gets in "Phoebe's Little Problem" say "Heyerdahl".
Not much is known about Phoebe's family, except that her father Kyo is of Japanese descent. In the Episode "Phoebe Cheats", her father said "Kampai!" (which approximately means "Cheers!" in Japanese) and is good at fencing, and her mother Reba has a strong Southern accent and is most likely from Kentucky. Her parents only had speaking roles twice: "Phoebe Cheats" and "Phoebe's Little Problem".
- Phoebe, like classmate Nadine, is of mixed heritage.
- Few fans of the show wondered if Phoebe wears shorts or not as it implied that her only clothing is her sweater (which is unlikely). However, there was an error in "Phoebe Skips" when Phoebe jumps there is nothing underneath her sweater. This rumor is somewhat debunked, by her 2017 design.
- A claymation version of Phoebe Heyerdahl "Friend" was featured 24 June 2018 in Robot Chicken's 175th episode.
- In "Hall Monitor", it's revealed that Phoebe hates Monster Truck Rallies.
- In ""Phoebe Breaks a Leg", it is revealed she is skilled at welding.