Any possibility it's some kind of campanula? They self-sow with abandon in my garden. The rosettes of campanula persicifolia look similar to your pic, though c.p. have pointed rather than rounded leaves.

They seem happy in your garden even if the color won't settle down! I would say the first and last are Laura, the middle picture probably is but often big grower container grown perennials are all hyped up on hormones and fertilizer that they don't look and grow quite normally in regards to height, branching, and color. I'm just thinking that my Laura never shows that large a white blaze in the center... Camera and perception can be very big factors, but some phlox go through major color changes depending on growing conditions. 'Laura' can lose the red part of the purple as it fades and appear more blue but temperatures also effect the starting color. Rachel Kane of Perennial Pleasures in Vermont sells and grows a ton of phlox, and if you browse her website you'll see her call these phlox 'changelings' due to the way they may start the day one color and then change as the day warms up. It's actually very interesting to see a blue phlox in the morning and then a purple at noon! 'Blue Paradise' is one that changes after a cool morning. A Hot spell may also change the color significantly. Hot weather will make most phlox produce paler flowers with less distinct centers. It's not until the heat breaks that the newer flowers will open in the darker shade. 'Blue Spot' does this in my garden. Here it is at the end of June when we were in the 90's with plenty of humidity and drying soil. (there's also a white phlox to the right and behind) Here's the same plant this morning. It's been rainy and only up to 80ish for the last few days.' (obviously the white phlox has gotten a little sloppier over the last month) .... what's really weird is when I scrolled back on this post, the dress went from being gold and white to being blue and black now!

I tried posting a reply several times with embedded images, but it keeps failing. Let me try sharing a little photo tour of my phlox with you this way (hope it works!) Meanwhile, THANK YOU for all of these great ideas! I am now really excited to browse Japanese sickles and/or hedge trimmers. I had considered using my string trimmer, but honestly I doubted its ability to stand up to the tough phlox stems. I also love the tarp idea and will definitely try that too. Another idea I had involves our mulching mower. Last year I ran over some of the beds in late November and was able to get it pretty well cleaned up. So if I sickle/trim the tops and let them fall, maybe they can just get mowed up later this year and compost in place?

I've been talking to a few people about Phlox paniculata jeana and it is basically sterile, so my comment about it growing true from seed isn't so truthful. I think the coming true from seed info came from a wrightup from Izel Plants. The story is that Jeana discovered 'Jeana' in her back yard that goes up to the river. She only found 1 plant. The 1 plant story makes sense because if it had been a whole colony, it would have been considered for a taxonomic placement as a subspecies or variety. It's still a variety, just not taxonomical. https://www.plantdelights.com/products/phlox-paniculata-jeana-summer-phlox