It certainly sounds pretty but I don't know if there is such a thing as a true red carpet phlox. There's one called Scarlet Flame but it's still decidedly magenta rather than red.

Squirrellypete

thats the one I was talking about - I'm a little disappointed its not really red. Might try it any way.

There is also a red creeping verbena (I think it's usually sold as an annual) that would be nice since they'd bloom with the roses