Kinda tough to tell for sure but it could maybe be "bright eyes" or "Franz Shubert" (see the picture in the link below) I think they look more Schubert...

Bright Eyes - http://www.whiteflowerfarm.com/36029-product.html

Franz Sschubert - http://www.insideiris.com/feature_plants/3671/Phlox__Franz_Schubert

I know my Bright Eyes have a much more purple color to them but they are definitely Bright Eyes..I'd say yours are one of the two...probably Schubert because of the way the flower coloring extends out toward the outer edge of the petal

Maybe a Jr. Surprise also?

Phlox definitely let off seeds like crazy...if you deadhead them regularly you could stop it (if you want to..I don't) as the seeds form in the buds after the flower has fallen off. The seeds look like little green beads/balls. I usually dead head part of the plant then leave the more non-visible stems alone so they can produce seed without the plant looking unsightly.

As per logixSTI, can't say.

Is it definitely garden phlox (Phlox paniculata) and not meadow phlox (P. maculata) which is also often that sort of colour?

To me, the colour (and vigour) might suggest a garden hybrid moving back in the direction of the (wild) species.

At least here, I see very little evidence of seeding with the recent well publicized garden phlox cultivars. I don't believe that this is simply the result of dead-heading.

Not Bright Eyes. Even allowing for faded image d/t sun, it is not pink enough or 'bright eyed' enough in middle.

It looks almost like what I have, labeled as 'Eva Cullum', but even Google images of this cultivar vary so greatly, it is almost unbelievable. Which leads me to think, many may just be seedlings of it...But, it could be as suggested above, the cv. 'Franz Schubert' which I do seem to recall, had a certain beautiful glow to it, later on in the day.
Many of my self seeded plants are either pure white, or appear similar to a named variety of the color of mutation of 'David'.
If you can locate a proper 'Blue Paradise' you might really like that one too.

Thanks everyone! It really does look more like a Franz Schubert. It really is hard to tell by the pictures online.