Question
live in zone 4-5, northern illinois, phlox plants in the yard grew well this year, but no flowers, we have lots of rain and hot weather, but plants failed to flower,

Answer
Hi Phil,
Thanx for your question.  If you're using a high nitrogen fertilizer, that could be preventing blooming and forcing the plant to concentrate all it's growth on green growth.  Lawn fertilizers leaching into the garden can cause this too.  The only other possibility I can think of is, has the sunshine level changed in your yard.  Is it shadier?  Less sun equals less flowering.  Does the plant bud blossoms at all?  I hope this helps.
Tom