Phlox paniculata definitely doesn't like extended dry periods in the summer, especially if they're not getting any afternoon shade, but you also might be overdoing it if you're watering them "every couple of days". Are you sure the soil has had time to drain in between waterings? When were they planted?

A lot of my paniculatas are looking pretty ragged in the dry heat we've been experiencing this summer. Powdery mildew is claiming most of the foliage, even on some of the more "resistant" cultivars, but my "Jeana"'s are actually among the few still looking pretty healthy and green.

I don't think it's a drainage problem because the more I think about I also have agastache blue fortune next to it and I would think if it's not draining it would be yellowing or showing signs of being to wer.

Although you can grow them together, the preferred cultural conditions are a bit different for your Agastache compared to the Phlox. Your Phlox will thrive more in a rich, moisture-retentive (but not soggy) soil with some afternoon shade, especially if your area is prone to hot/dry spells (which your Jeanas are suffering from already as Floral pointed out.)

The Agastache will do best in a more free-draining, poorer sool in full sun.

So, in essence, a spot where the Agastache is happy might not be the ideal spot for the Phlox (unless you want to be watering regularly through the summer). I grow plenty of both of those plants in my garden, but nowhere right together.

if you water every 3 days.. and your plants droop in between.. how about you water every day.. or every other ...

in my MI.. its been so hot and droughtlike.. i have had to water TWICE A DAY in my sand ..

ken

and.. if its only these.. and you dont want to water more.. then out they go. shovel prune them.. and be done with it.. this is usually the cheapest alternative ... one time labor.. and small digging cost.. then presto.. never a problem again from them.. and good riddance .. you will bend to my will or be gone... out out dam-ned spot ,... throw in a little shakespear to edumacate you peeps .. lol ..

ken

I was trying to be judicious with the watering when we were starting to notice effects from the heat and the drought, but as it went on longer and longer, the trees around me suck all the moisture out of the soil to survive and it just wasn't doing much good to water when the next day or two, it was dry again. I've been watering every day for the past 2 weeks, anything that was dry again and it's been a lot to keep up with. I have some ferns that are flat on the ground even after watering, when they were thick and lush in the spring. I think I waited too long to water in a few instances. I do see a few new fronds coming up in the middle but, they have had quite a set back.

Even my Agastache are struggling. Not wilting, but brown leaf edges and flowers that are barely lasting a few days.

Common phlox (phlox paniculata) is a wet land plant native to the SE. Short of trying to make it a true aquatic, you're not going to overwater it.