According to the Fifth Doctor's quotation of the Bible, Phoebe was a deaconess of the church at Cenchrea. She was an assistant to Paul of Tarsus whom the apostle mentioned in his letter to Rome. He used the quotation in order to explain to a guard why he should be allowed to have female clerks — Peri and Erimem — attend him in the Council of Nicaea. (AUDIO: The Council of Nicaea)
Behind the scenes
In order to make his point, Davison quotes Romans 16:1, though it's a little unclear what version of the Bible he's using, or why he seems to add a third syllable to the name Phoebe.