Do you mean phlox? Here's an article with a lot of great information. Wishing you the best.
you can try cutting it back (by about 1/3) and giving it a good dose of fertilizer. Flax is a flower that loves feedings. Be sure to water it in this heat too. Might rebloom for you in a few weeks.
I see that you changed the spelling so that is now clear that you mean flax. I would agree with Dianne. Cut it back partway and give it some fertilizer. It should rebloom again this summer. Wishing you the best.