Phlox have shallow roots, so I'd try watering, pruning, and shading them for a little while until they recover. Also check for insects at the base of the plant. Right now, the earwigs are eating everything here, and they are on my hit list.
Good luck!

Mary

Hi Joe,
Are you having trouble with creeping phlox or the tall ones? The creeping phlox tends to die back this time of the year. If it is the tall phlox , I'd agree with Mary. I have also cut back my tall phlox when it has gone into a slump, kept the soil moist and they tend to come back fully.
Jo