Not an expert, but creeping/carpet phlox's botanical name is phlox stolonifera. The root of the species name is stolon. Stolons are above-ground stems that root at the nodes. So that answers your first question. If the mulch is thick (like pine bark nuggests) and deep enough it could potentially impede the spread, but I would look to other factors first.

Newly planted perennials often focus on root establishment the first season before spreading, so I wouldn't be alarmed. If it is leggy, it may not be getting enough sun. Some creeping phlox cultivars tolerate more shade than others. I don't know which cultivar you are dealing with.

Let me clarify the confusion that I just created above: Phlox stolonifera is creeping phlox that is native to woodlands and likes shade. It spreads by stolons.

Phlox subulata is known as moss phlox and likes full sun.

I am not sure which you have, but they both spread from creeping stems (stolons). Sorry for any confusion.

Lol, thank you. I have Phlox Subulata. Maybe it isn't getting enough sun? :( I am new at this, so forgive me. I planted them as a border in my front garden beds that are mostly shaded by 2 large trees. It's not heavy shade...I'd say dappled, with portions of it getting straight morning or afternoon shade. The plants that get straight sun are just as leggy as the ones that get only dappled sun, though I would say they are a darker shade of green. My problem with this border is that I haven't been able to find something that would be happy in all the various levels of sun that this border gets, and I went ahead with the decision to plant the Phlox based on comments from a few people that my Texas full sun is much more intense than full sun in other areas, and that it would be more than ok. It may be fine and is so hard to tell right now, since it is still so new. I wish I had a crystal ball or something so I wouldn't have to waste so much time waiting on something to fill out, if it has no intention of doing so. Ha! I struggle with patience, can you tell? Clearly I'm going to have to find some or choose a different hobby. ;)

Thanks for the info. You have been helpful. Oh, and I will need to monitor my mulch. It's shredded, but thick since again...Texas! I've been here most of my life and every summer I say "I seriously don't think I'll survive another summer here" And yes, I'm plenty old enough. Lol.

I suspected you had subulata since "moss" and "carpet" are pretty much synonymous. The reason I got the two mixed up is because both species spread via stolon.

There is definitely some experimentation that you have to do with this, but from my limited experience moss phlox needs a decent amount of direct sun -- especially when they are blooming and growing in spring. So if under deciduous trees, you may be okay. I assume you live in North/Central Texas. I don't think the sun is so intense there that moss phlox would prefer less than full sun. The real test will be how profusely it flowers in the spring. If it is spotty with flowering, you will know it isn't getting enough light. I still think the plants are getting established and will turn their attention to spreading once the roots have gotten their act together.

You may want to give this thread a go in the Perennials forum because this one is less heavily traveled than that one. Good luck!

Thank you again. I think I will give the perennials thread a go, just to see if I can catch someone who has grown it with my circumstances. Maybe I'll get lucky. Again many thanks, you have given me a lot of info and I appreciate your kindness. :)