In Douglas Campbell's new reading of Romans (in The Deliverance of God) he assigns a significant role to Phoebe in communicating the "speech in character" aspect of large parts of Romans 1-3. This was mentioned by DC in the Q&A at SBL (audio recording here - about 75% through); but comes up only once in the book, and there without any discussion:
"it seems fair to suggest that Romans 1:18-32 could have been performed as speech-in-character. (And had Paul composed this passage in this way, he presumably would have given Phoebe explicit instructions in how to perform it.)" (p. 532)It is surprising that considering the importance of this performative possibility in DC's reading, his presumption is not explained or defended in any way. It is worth noting that there is less evidence for letter carriers involvement in reading/performing the letter which they are carrying than Campbell presumes here (for the documentary papyri see my JSNT article).