Any of several beetles feed on garden phlox. One of the more common types is blister beetle. These can be controlled with applications of Sevin.
Phlox plant bug attacks the upper sides of tender leaves and buds causing white or light green spots on the leaves. Remove infested plant parts. No chemical control is listed.
Four-lined plant bug causes round, brown, sunken spots on the leaves. No chemical control is listed.
Mites cause the foliage to lose its green color. Heavy infestations form fine webbing. Spray with rotenone.