The demon Phenex appears in the grimoires Book of Incantations, The Discoverie of Witchcraft, The Book of Spirits, Pseudomonarchia Daemonum, and The Lesser Key of Solomon
From The Lesser Key of Solomon, Crowley/Mathers edition:
The Thirty-seventh Spirit is Phenex (or Pheynix). He is a Great Marquis, and appeareth like the Bird Phonix, having the Voice of a Child. He singeth many sweet notes before the Exorcist, which he must not regard, but by-and-by he must bid him put on Human Shape. Then he will speak marvellously of all wonderful Sciences if required. He is a Poet, good and excellent. And he will be willing to perform thy re-quests. He hath hopes also to return to the Seventh Throne after 1,200 years more, as he said unto Solomon. He governeth 20 Legions of Spirits. And his Seal is this, which wear thou, etc.