Certified GKH Gardening Expert
You are in hardiness zone 6 so the cold winter should not have affected it. (generally hardy to zone 3)
Shaving the mound to remove some of the older, woody growth should help with the flowering (you can mow it on high setting after flowering). Also, there are two types of low growing phlox, p. subulata and p. stolonifera, and the subulata type requires full sun to perform well. The other blooms in part shade or sun.
Repeated bouts of powdery mildew can weaken the plants and reduce flowering. Full sun and good air circulation decreases the chance for such fungal diseases.