Can I trim it back in the summer to try to rejuvenate it?
My Creeping Phlox Is Splitting and Turning Brown in the Center
Certified GKH Gardening Expert
You can try giving it a pruning. It is as simple as taking an inch or so off the top, just like a haircut.
I would also try treating it with a fungicide and make sure that it is getting enough water too. In many areas, it has been a hot, dry summer and it may just be going dormant due to this but it also may be a fungus attacking the plant.