Answer: I'm confused about the true identity of your plant. Thrift is Phlox subulata. It requires well draining soils. If the plants remain too wet for too long, the foliage will yellow. I'd be careful with the watering.
Armeria is Sea Thrift. It is not as heat tolerant as phlox so I expect that when the weather cools a bit it will perk up. Some plants just don't appreciate the the Texas weather!
Q&A Library Searching Tips