Phoebe Hyerdahl is a fictional character in the animated series Hey Arnold!. She's Helga's best friend and sidekick, as Gerald is to Arnold. She was voiced by Anndi McAfee for the entire run of the series.

Note: Some minor plot details follow.

Phoebe is characterized by her brain: She is among the smartest kids in the entire school (she was given a free pass to 6th grade in "Phoebe Skips" in recognition of this fact). Her distinct features are a huge lump of black hair at the top of her head, a small yellow scrunchie on her hair, and, as is the stereotype of smart kids in animated shows, her big blue eyeglasses, short stature, and squeaky voice.

Among her most notable moments was when she won the City Academic Bowl, a competition that by all means she shouldn't even have been competing in, as Helga (in her attempt to win the only trophy her big sister Olga never won) had won her school's spot at the Bowl by forcing Phoebe to miss the final question ("Phoebe Takes The Fall"... ironically, McAfee did not receive a credit for the role in that ep). At the opposite end of the spectrum, she was utterly humiliated by just about the entire student body ("Phoebe's Little Problem") when she was caught farting on the stage at the school auditorium as she was receiving an award, and subsequently refused to ever go to school again (ironically, the award was for her perfect attendance). Among other achievements of Phoebe's include winning the Parents Tournament Weekend with her parents ("Parents Day"... none of the Hyerdahls had speaking roles in that ep, oddly enough) and the City Go-Kart Grand Prix with Helga and Harold ("Grand Prix").

Not much is known about Phoebe's family, except that her father Kyo (George Takei) is of Japanese descent and is good at fencing, and her mother Reba (Jean Smart) is most likely from Kentucky (in "Phoebe Cheats", this is where Phoebe says she is from). Her parents only had speaking roles in two eps: "Phoebe Cheats" and "Phoebe's Little Problem".

There is a question of whether Phoebe's classmate Gerald has a crush on her. See here for more details.

Trivia: Anndi McAfee and Francesca Marie Smith (voice of Helga) also play best friends on another show, Recess, as two of the members of the Ashley clique. One of the creators of that show, Joe Ansolabehere, also wrote for Hey Arnold!.