Desperate Housewitches - S8-E4
Continuity mistake: Paige asks how The Source was previously vanquished, but she was there both times: when the original Source was vanquished, and again when they vanquished Cole. Also Phoebe wasn't actually there for the final vanquish of Cole, but was taken back by Cupid as if it was her memory.
Chosen answer: Her agent/manager negotiated a special billing as part of her contract. It distinguishes her from the rest of the cast, probably when she became a producer on the show.
JC Fernandez