Dahlias (haven't grown for years), typically peaked for me around frost time...as I recall. They did exceptionally well as things cooled down and got a bit wetter.
Phlox are pretty much done and toasted by now....esp with powdery mildew issues.

If you want fall flowers, plant asters, or annuals like cosmos bipinnatus (also tend to just get bigger and better till frost). Some perennials like rudbeckias, goldenrods, and salvias are the main power houses till frost, but perennials get tired and spent after a period of bloom, after all nothing lasts forever.

Thanks, dbarron. I need to cut what I have, and see if they won't come back. I have not been good at pruning the dahlias, and some of the phlox plants were too small when I purchased them, and they never took off. I don't seem to be able to find many fall plants now in the discount stores. It looks like I will have to drive over to a nursery where I can find some fall plants.

Sammy