Below is a simple Phoenix in flight in a rainstorm. I later added a stag and cat (or any other creature) for a sense of scale and for some interaction between the two creatures.
Researching on the Internet for bird references I came across images of herons and secretary birds standing on freshly caught prey. The white elegant secretary bird conquering a dark serpent could almost be poetic. Here is the same sort of idea, a radiant Phoenix standing on a defeated dark creature, which in this case was made into a dragon. There is mist in the background to add some mystery.
A low point perspective of a screeching Phoenix on some sort of building/tower, as if summoning the vortex of clouds above. In another thumbnail there is some ivy crawling up the surface to give the building a decaying old look, as if the civilisation that built it has long since perished and this building now only serves as a roost. The third is a bit more destructive, with lightning hitting the tower with plumes of fire coming from within.