Mary,

Thank you for your question.

From the photos you shared, I believe that your phlox may have spider mites.  These can be a problem in drier areas or during droughts.  I'm including a link to a good article on this issue that shows you what to look for to confirm that this is the problem - and it also has suggestions for how to treat the plants.

https://extension.sdstate.edu/spider-mites-garden-phlox

I've also copied the information from the article and put it into the file attached if that is easier for you to access.