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 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.