Hi Bill,

From what I can see in the photo, that is Dame's Rocket (Hesperis matronalis).  It's sometimes also called "spring phlox".  

It was at one time a popular choice for cottage gardens; however, it has proven to be quite weedy and is listed as a noxious weed in several states, including Colorado, where it is a "list B" weed.  https://ag.colorado.gov/conservation/noxious-weeds/noxious-weed-species-id/dames-rocket

List B weeds are designated to be managed for containment to keep them from spreading to new areas; the plants in your yard should be removed if possible.

I hope this is helpful,

Cordially,

John