There are 2 kinds of Phlox that thrive in shade, Phlox divaricata and P. stolonifera. Look at the bottom of the plants. If you see shoots coming straight out, that is stolonifera. Those are stolons, which is how it spreads. If it does not have stolons, then it is divaricata. Divaricata is also taller than stolonifera. I have no experience growing stolonifera, but I have grown 2 varieties of divaricata for years. P. div. is best in part-shade in moist garden soil. It is evergreen and should be divided in Spring. Here it blooms most of May, but the foliage is attractive the rest of the year if it is deaded down to the basal foliage after flowering.

Thanks a lot, Entling. It is the shorter one, I think, the stolonifera. It's about 8" tall now. When I plant it, I'm thinking of cutting it into 3"x3" pieces. I've got clay and am used to double digging and amending for large perennials. How much prep work do you think I need and how deep will the roots grow? Thanks again!