I've had gorgeous ditches of creeping phlox and have given away big clumps of it. I've found that it needs LOTS of water during the first summer to get established. It died for several people I gave it to, but it spread around my culvert in gravel with no effort on my part. So I would suggest get another good-sized clump from your grandpa, plant it in part shade (until it gets established--maybe a year or two), water it heavily, especially the first year. Then when it is established, move it to direct sun and water heavily again. I've moved clumps to new areas and it seems the ones I put in partial shade take hold sooner than those in direct sun. Good luck.

I've had the best and worst luck transplanting and sharing creeping phlox over the years. I found that timing is everything. The best time is just after the flowers start to fade. If you watch the forecast for overcast rainy days in the latter half of May (zone 4/5) you should have no problem. When I first started mine from my husbands grandmother I grabbed a handful flowing onto her cement sidewalk that wasn't even rooted and it took right off. Even though your best bet is next Spring it's worth experimenting now. Virginia is right. Don't let it dry out while being careful not to give the roots mold disease _and turn a lawn chair over it or something to keep it shaded until it takes. Good luck!