Posted: 17/08/2013 at 12:44
Assuming they are perennial phlox paniculata, and not the annual bedding phlox, deadhead them. They may give a second flush, but only in very good conditions. Usually they will go yellow and the leaves fall off and they become dormant for the winter. I tend to leave the stalks on until spring, when they start growing, and then cut the old stalks down to the ground. That way I don't forget where they are and put the fork through them.