Phillips is best known for once being married to Peter O'Toole and her performance as Roman empress Livia in the British miniseries I, Claudius (the wife of Brian Blessed's Emperor Augustus). She also appeared as the Reverend Mother Gaius Helen Mohiam in David Lynch's science-fiction epic Dune. In the BBC miniseries adaptions of Tinker, Tailor, Soldier, Spy and Smiley's People, she plays the wife of Alec Guinness' character.
In 2000, Phillips was awarded the honorary title of Commander of the British Empire for services to drama.