Green Phoenix: The Last Stand of the Prehumans is a novel by Thomas Burnett Swann. According to Wikipedia, it is based on the novella “Love Is A Dragonfly” published in The Magazine of Fantasy & Science Fiction from March 1972. It was published by DAW Books with cover art by George Barr.
Author’s name and title set in Corporate Image, which was released the year before. Subtitle looks to be set in an all-caps Eurostile.