any chance at some pix?

OK, i'm posting a picture with great mortification because it looks so awful! You can see the hydrangeas in the rear, then a gap where I cut back the dayliles, then taller DL growth in front that were cut back at a different time, and then the now flopping phlox. I wish I also had a picture of the area when all three are blooming simultaneously because it is actually stunning. But then this. What's the solution?

Ahh don't be mortified- it's just part of the experimentation that gardens all go through.

So anyway, I've planted both tall Phlox and Dallies in a perennial bed and I ended up eventually separated them. (My Phlox is Blue Paradise and they also flop) The dallies overwhelmed them wanted to spread and mature.

I'm having a hard time understanding what I see in your photo which is a bit blurry. I don't understand why you are cutting back foliage on your dallies and phlox in the growing season? Did I read that right? Let it grow. If it's too crowded don't cut back- instead dig up and move.

From what I can make out in the photo I would first define my garden bed with a sharp cut edge made with a shovel- then add mulch to keep it separate from the grass.

If it were my garden and I had to combine Daylilies with Hydrangea and Tall Phlox I think I would clump the phlox off away from the Dallies- their shapes just don't combine well visually.

I would probably choose to plant the tall phlox in front of the hydrangea bushes...and dedicate a flower bed to the dallies because of their "fountain" shape that spills out and over other perennials of even the same size.

Or plant the daylilies in front of the Hydrangea and place the tall phlox in another flower bed with some other perennials, such a purple cone flowers that would sort of support them or alone with maybe a wire garden support because of flopping issues.

Here is a link for companion plants for tall garden phlox that might inspire you https://www.gardenia.net/plant-combinations/plant-family/phlox

So helpful, Sue. Thank you! I cut back the daylilies when they got ratty looking so that I could stimulate fresh growth. The hydrangeas look good throughout the season so daylilies are perhaps a poor choice of companion. Phlox lasts much longer. Unfortunately the day lilies are now too extensive to move so it’s the phlox that goes. Agree that neatening the bed will help a lot. So would treating all the daylilies uniformly, whether rather than a few at a time.