Creeping phlox grows best in full sun in a well drained soil. Plants grow well in sandy or gravely soils and tolerate hot, dry exposures better than most other species of phlox. If the soil is not well drained, the plants will decline. Make sure mulch is thin and away from the base of the stems. They grow best in rock gardens, on slopes, etc. 

In general, phlox can limp along after flowering. You can cut back the stems after flowering by 1/2 to maintain form and promote denser growth plus to stimulate a possible light rebloom. Prune out any dead brown growth and monitor for additional symptoms.

Marian