Phoebe is mentioned in only one place in the Bible:
I commend to you our sister Phoebe, a servant of the church at Cenchreae, that you may welcome her in the Lord in a way worthy of the saints, and help her in whatever she may need from you, for she has been a patron of many and of myself as well. (Rom 16:1-2)
Paul describes Phoebe as both a “servant” [διάκονον] and a “patron” [προστάτις].
The word διάκονος usually refers to a servant (cf. Matt 22:13) but is also used as technical term for a specific role within the church, usually rendered “deacon” (cf. Phil 1:1; 1 Tim 3:8ff). Whilst it is possible that Phoebe is a servant in the general sense of the word, since she is specifically named as a διάκονον of the church at Cenchreae it is likely that the word is used here in the technical sense. This indicates Phoebe held a special function within the church, like that described in 1 Tim 3.
The word προστάτις is only used once in the Bible, so we do not have other verses for comparison. It is translated “patron” (ESV), “helper” (NASB, NKJV) and “benefactor” (HCSB, NIV). Outside the Bible related words are used to refer to leadership or roles of authority (see Liddell & Scott), so it has sometimes been suggested Phoebe presided over the services at Cenchreae. However in context this seems unlikely. Paul is requesting the Roman church helps Phoebe because she has helped many, including himself. Therefore it is likely that προστάτις describes the way in which Phoebe helped others. It seems more likely that here προστάτις refers to a female patron, just as the male equivilent (προστάτης) can refer to a male patron. The most likely option is that Phoebe was a wealthy women and provided for the needs of those at the church at Cenchreae.