But which species of Phlox do you mean? There are alpine ones which grow to no more than 3 or 4 inches( P. douglasii), and there are herbaceous ones which grow to 18 inches or so(P. bifida) and there are tall ones (P. paniculata). There are also annual ones. And if they were still available there is P. mesoleuca with WOW! factor to spare.

Hi I am looking for a medim sized one so about 18 inches or so, I can go bigger and prefer a summer flowering one. Thanks

Best 18 inch tall one I know of is P. divaricata Clouds of Perfume. Beautifully scented blue flowers. But wow factor is possibly a little lacking. Another choice might by P. carolina Bill Baker which is a good pink form.

Phlox paniculata bright eyes is one of the best and a little taller at around 24-36 inches.