Unfortunately, we can't tell from the close-up photo what is causing the plant to struggle. Can you send more pictures of its overall condition or describe particular symptoms? Some of our native Phlox species prefer growing in full sun while others prefer semi-shade or mostly shade (woodland conditions). Blue Phlox can be a common name used for Wild Blue Phlox (Phlox divaricata), and if so, it will not thrive in a full sun location. Do you have an area receiving some dappled afternoon shade it can be moved to?

Is it being checked for watering needs during this prolonged drought? Your county isn't as dry yet as other parts of Maryland, but locations in home gardens can still be drought-stressed given or insufficient rainfall. Wild Blue Phlox prefers to stay more evenly moist (but with good drainage) and may be stressed if allowed to get too dry.

If there is foliage missing from sections of its stems, rabbits (and sometimes deer) are known to eat Phlox, so that could be part of the problem if the plant appears to be shrinking and not establishing. Depending on what size of plant you installed (seedlings, a plug, or a larger pot), it can take some time to establish roots and fill-in with fuller growth.

Miri