It's evergreen. it makes a needly-looking mat. Very neat and clean. It would make a good ground cover, esp if you underplanted with some small fall and summer blooming bulbs to liven things up when it isn't blooming.

The big boxes like Lowes will have a huge array of ground phlox in the early spring. It spreads nicely here in full to part sun, but it doesn't like to be shaded too much by other plants. This has been my experience, but I do not have full, full sun anywhere.

I agree with puppyscruff. I mostly have part sun and it does fine, but it will lose it's leaves and die out in that spot if it gets overshadowed by bigger plants for too long. It roots as it goes, so it just keeps on growing in the spots it likes. So if you did plant bulbs make sure they are small stuff that won't overshadow it- like fall crocus or stuff like that.