Phillips' music career spans more than 30 years. She came to prominence in the mid-1980s as the singing voice of the title character of the animated television series Jem. She has also been a member of the bands Luna and as one half of the duo Dean & Britta, both with her husband Dean Wareham, and has had a solo career which has included one studio album: Luck or Magic.

Britta's first acting job was as the singing voice of the lead character in the animated series Jem, alongside Actress and singer Samantha Newark, who provided Jem's speaking voice. The series ran from 1985 to 1988.

In 1988, she co-starred in the teen rock band movie Satisfaction, also starring Justine Bateman, Julia Roberts, Liam Neeson, Trini Alvarado and Scott Coffey. Phillips performed several songs during the movie and is featured on the Soundtrack album. Also in 1988, she guest-starred in an episode of the cult TV show Crime Story, in which she played a former homecoming queen turned high-class escort in Las Vegas, Nevada ("Always a Blonde"). She followed that with a starring role as a nurse in the pilot episode of the short-lived TV series Nightingales. From 2005 to 2008, she voiced various characters for the Adult Swim series Moral Orel, most notably as Bloberta Puppington. In 2006, she featured as herself in the Luna band documentary Tell Me Do You Miss Me. Since 2010, Phillips has voiced various characters in Mary Shelley's Frankenhole, most noticeably Elizabeth Frankenstein. Both Moral Orel and Mary Shelley's Frankenhole were created by Dino Stamatopoulos. In 2010, Phillips appeared alongside Wareham on Yo Gabba Gabba! in the episode titled "Ride".

Phillips was a member of the bands The Belltower and Ultrababyfat in the 1990s and Luna from 2001 to 2005. Since then, Phillips has released albums with fellow Luna bandmate Dean Wareham as the duo Dean & Britta. Wareham, a former member of the band Galaxie 500, toured with Phillips in 2010 performing the band's back catalog. Phillips has also toured with Ben Lee. Phillips and Wareham have also composed original score for the Noah Baumbach films Mistress America and The Squid and the Whale and the Morgan J. Freeman film Just Like the Son. Their song "Knives From Bavaria" (Sonic Souvenirs) appears in the Olivier Assayas film, Clean (starring Maggie Cheung). Their song "Your Baby" appears in the Italian movie "A/R Andata e Ritorno", directed by Marco Ponti.

In 2001, Phillips provided vocals on the Anika Moa album Thinking Room. In 2007, Britta produced and recorded a cover of Neil Young's "I Am a Child" for the benefit CD Cinnamon Girl - Women Artists Cover Neil Young For Charity. In 2010, Phillips performed vocals on the MGMT single "It's Working" from their album Congratulations. 2016 saw the release of her debut solo album, "Luck or Magic" on April 29. It contains 5 covers along with 5 original songs.

Phillips married musician Jody Porter but the couple divorced. In 2006 she married musician and Luna bandmate Dean Wareham during the recording sessions for their album Back Numbers.

Britta had a cameo, along with Dean Wareham, in the 2012 Noah Baumbach film Frances Ha (written by Baumbach and Greta Gerwig).

Phillips appeared on Ken Reid's TV Guidance Counselor podcast on December 9, 2016.