Sherwood Purple Phlox spreads well and does keep a nice mat of foliage, and doesn't mind shade, so that does sound like a good choice. Is it a dry area? Mine spreads better in areas with more moisture, but I do have a lot of tree root competition, so some are in dryer spots and doing okay. If it is dry, you may want to plant more of them, closer together, so that you don't have erosion while waiting for them to establish. Vinca minor has been added to the exotic invasive list for KY, so I've been working on removing it. I always liked it, even though it could be troublesome, but in your zone and that situation, it sounds like a good choice, especially if you won't be doing much other planting there.
