Powdery mildew.

In my experience, powdery mildew if bad enough will kill off the lower leaves just as in your photo. If desired for appearance, you could remove those brown leaves (into a plastic bag for trash disposal, not compost pile) and then plant some annuals in front but not too close to the phlox.

Next year, thin out some of the crowded stems - cut off right at the base -- early to allow for more air circulation. Phlox do like water, tho not from above -- hold your hose sprayer down nearly at ground level and use the "flood" or "soaker" setting.

I would cut them back and make sure to water them well.

Thank you to everyone for your thoughts about this. It's so sad for me to see them so afflicted. I've had them for years and watered them from "above" without any problem but this year they succumbed to my poor watering techniques and got hammered with this mildew. I know soaker hoses are the way to go. My sprinkler guy does not use them but prefers "drip" hoses. Any opinions about this from you all? I really want to make things right. Are drip hoses not as desirable as soakers?

I've given up on garden phlox for the very reason you cite above. They're planted in my garden beds but I leave them to survive--or not--on their own.

Don't be too discouraged, it's still not too late to thin that bunch out. I'd remove all the weaker stems (probably about half of the total, and then give them a drink with liquid fertilizer.

The mildew.... Someone suggested a 1 part milk 9 parts water spray in the other phlox post. I think that was the ratio and it's definitely worth a try if you'r a milk drinker and have it on hand already.

There is not enough air flow, they should be thinned out now.

We water gardens phlox from above, but thinning out allows the water to reach the soil surface.

We have no problems eliminating powdery mildew with phlox paniculata, I'm wondering whether it's maintaining Phlox paniculata in southern gardens which is the challenge.

sunnyborders(5b), how are you eliminating the powdery mildew? And I wonder why you're not having problems with it as you too are watering from above. Am I understanding that thinning it out prevents the mildew?

Everyone's comments are SO helpful.

Two other threads to check out:

http://forums2.gardenweb.com/discussions/4726411/im-giving-up-on-garden-phlox?n=25 is a discussion of mildew and phlox and

http://forums2.gardenweb.com/discussions/4727892/phlox-2017?n=13 has a link to the Chicago Botanic Garden's evaluation of phlox.

Be sure to clean up the area well in the fall, cutting the plants to the ground and putting all the fallen leaves and old stems in the trash since the mildew spores winter over in plant debris.

Soaker hoses and drip hoses get great praise from people who don't have creatures. Something - bunnies, moles, groundhogs, squirrels, raccoons - you name it we have it - make mincemeat of both soaker hoses and drip arrangements. Water by hand or overhead and use the mildew formulas.