In the pilot episode, Phoebe is introduced as one of the six original friends, including her Greenwich Village Manhattan neighbors Joey (Matt LeBlanc) and Chandler (Matthew Perry), former roommate Monica (Courteney Cox), Rachel Green (Jennifer Aniston), and Monica's brother, Ross (David Schwimmer). She is a masseuse and part time, aspiring folk-type musician, who plays dreadnought style acoustic guitars and sings very awkward or absurd, self-composed songs. She has been shown busking in the subway, outside of the gang's usual "hang out" place, Central Perk, as well as at a public library, and has been seen frequently playing live sets inside the coffee shop. She had moved in with her maternal grandmother (Audra Lindley), upon moving out of Monica's apartment, approximately one year before the pilot episode, due to Monica's obsessive compulsive nature and anal-retentive cleaning habits. During the first season, she has myriad boyfriends, including Tony, a physicist named David, played by Hank Azaria, and a psychologist named Roger, played by Fisher Stevens. Phoebe works as a temporary secretary for Chandler for a brief period of time in "The One with the Ick Factor".
Phoebe's crass, identical twin sister, Ursula Buffay (also portrayed by Kudrow), a character originally created for and appearing in the American sitcom Mad About You as a waitress, is also introduced in the first season, in "The One with Two Parts". Phoebe is shown to have a very strained relationship with Ursula who is one minute older than her and seems to care little about family affairs or Phoebe, Phoebe nearly always goes home empty-handed and none the wiser. When it is revealed Ursula performs in porn under Phoebe's name, Phoebe eventually finds some redemption by cashing in Ursula's pay slips. Phoebe's father, Frank Buffay, abandoned the family when Phoebe was a child, and the woman Phoebe believed was her mother, Lily Buffay, committed suicide when Phoebe was about 14, by means of carbon monoxide poisoning. However, Phoebe discovers she has a paternal half-brother Frank, Jr., and later meets her real mother Phoebe Abbott (Teri Garr), who had given her up for adoption when she was born.
In the second season episode, "The One with Phoebe's Husband", it is revealed that Phoebe was legally married to a "hoping to be gay" Canadian ice dancer, Duncan Sullivan (Steve Zahn), for six years, to help him acquire his green card. The two divorce when he realizes that he is, in fact, heterosexual, and going to marry another woman. In "The One with the Baby on the Bus", Phoebe is temporarily replaced as the primary singer for Central Perk by a professional singer named Stephanie Schiffer, played by singer Chrissie Hynde. Phoebe's song "Smelly Cat" is introduced in the same episode. In "The One Where Eddie Moves In", a record company produces a full budget music video for the song, in which her voice is overdubbed by a much better singer; she turns down her record deal when she discovers the depth of the deception.
Although the facets of Phoebe's character are manifold and extremely complex, Phoebe can generally be classified as kind-hearted, but ditzy and whimsical. Due in no small part to her extremely traumatic childhood, Phoebe has developed a child-like naïveté in an attempt to shield herself from the world's evils. In addition to being a vegetarian and an avid tree hugger, she also displays a remarkable lack of experience with the "darker sides" of life. In "The One Where Old Yeller Dies", it is shown that her deceased mother Lily would turn off films before a tragic ending, including the death of Old Yeller or Bambi's mother being shot. It is also revealed that she was never told the truth about Santa Claus. This is made all the more prominent as one of the running jokes of the show is Phoebe's seemingly infinite criminal record. She repeatedly makes reference to her underworld connections and crimes committed while living "on the streets".
Much to the dismay of her friends (especially paleontologist Ross), Phoebe dabbles in trendy New Age ideas and superstitions throughout the series. She is convinced she can feel the presence of her dead grandmother in her old apartment, she senses the spirit of her mother in a lost cat, reads tea leaves, and dismisses Charles Darwin's theory of evolution as "too easy" in "The One Where Heckles Dies". Very in tune with her emotions and those of others, Phoebe sometimes serves as a rock to her friends. She especially shows a great deal of maternal instinct towards her younger brother Frank, despite the latter's lack of intelligence.
Similar to the short-lived Monica/Chandler/Richard love triangle, Phoebe had two serious romantic interests that overlapped with each other at one point during the series. Physicist David (Hank Azaria), has a romance with Phoebe in the first season of the series, but breaks her heart when he decides to leave for Minsk on a three-year research trip. He makes a few more appearances throughout the series, most notably shortly before her engagement to Mike (Paul Rudd). Mike was introduced early in the ninth season of the show, during a double blind date with Joey, who finds Mike randomly at Central Perk. After a whirlwind romance, Phoebe and Mike break up after he says he never wants to marry again, and she briefly reunites with David. While on a trip to Barbados, both men propose to her, but she rejects David, realizing she is in love with Mike. She temporarily rejects Mike's proposal also, merely wanting an indication that their relationship is progressing. She ends up marrying Mike.