BONAP's North American Plant Atlas indicates 65 species of Phlox in the U.S. with four species of Phlox native to Iowa.
Two other species (P. paniculata (garden phlox), and P. subulata (moss-pink phlox) are occasionally found to escape cultivation. Neither is a native Iowa species.
Phlox bifida - Cleft phlox
Phlox divaricata - Wild blue phlox
Phlox maculata - Wild sweetwilliam
Phlox pilosa - Downey phlox