My stoker/wife got this lovely "phlox" at a garden club sale a year or two ago and it was going great in our backyard.
Saw an article in the Indy Star last week describing the nasty invasive Dame's Rocket, which is what our "phlox" really is. We cut it down and poisoned the roots.
Dame's Rocket has 4 petals on the bloom, while phlox has 5. Note the 4 petals.


http://na.fs.fed.us/spfo/invasiveplants/states/in.asp