It's Fall and only a few blooms remain on the tall garden phlox. Should I cut them back to their crowns now so they will bush out fuller in the Spring? I have already mulched the two flowerbeds in the front but if I cut them back, should I mulch around them again? I guess I should pull up the plant support rings I have around them and store them inside to protect them from the winter elements? I haven't looked to see where the seeds are. Maybe I should do that before I cut them back.
Cutting back is more of a personal choice, I usually leave above foliage to help trap snow to the plants for winter moisture. Phlox are pretty good about multtipling, if ya wanna speed up the process can clip back tops and sink in potting mix to root. Could cut stalks into peices, just make sure which end is up on each peice. Also phlox can be increased from division and or root cuttings (cut root pieces from mother plant and lay on side in hole. Also if dug and moved many of the roots left in the ground will sprout, Got dozens of new David phlox this year from doing such. And the seeds may sprout and grow for you. Good Luck. Kathy.
You could cut back your phlox now, but I don't know that it would do anything to increasing your phlox next year.
I do know my MIL stuck a peice of phlox into the ground and it rooted and grew for her, which follows Kathy's suggestions.
Myself, I always use division. It takes a year to two for the plants to increase in size. I have never had to use support rings for my phlox plants either - they tend to be sturdy plants, however there is no reason you cannot put support rings around them if you would like. I have offered up phlox seed in trades, however I question whether the plants from the seeds would grow true to the mother plant.
Next year when the new stalks are about 1' tall, pinch them back by 1/3. It will make a bushier plant. Cutting them back to the base now will not. Keep in mind they will be a little shorter---not too much, but much bushier.