Which kind of Phlox, Izzy? There are several species used as ground covers.

Not sure, Tugbrethil...I'll try to find out! They were sold just as ground cover Phlox this time last year on Thompson and Morgan's site...see they are advertised again now!

Phlox subulata and phlox douglasii.....does that help?

Well, I know that P. subulata needs at least 6 hours of sun a day to bloom well, but I'm not familiar with P. douglasii....My research shows that it also needs sun. Both are apparently alpine-type Phlox, so they also need gritty soil. Are they maybe in rich soil under a shade tree?

No...they are in full sun, on the whole. They look very healthy but perhaps they need more gritty soil! My soil is very sandy...should I add extra grit around them?Perhaps I'll see what happens next year ? Thanks Tugbrethil.

Sand should work the same as grit, Izzy, unless it's a very fine sugary sand. Are they showing any other symptoms, such as loose, feathery growth with long spaces between the leaves? Did they show any signs of making flower buds, but the buds just didn't grow? Usually bloom is sparser the first year, but there still should have been some. Puzzling! : /

I have just come in from school but I'll take a photo tomorrow. They seem to have very healthy growth, not loose or feathery as suggested. It baffled me, I must say! I kept waiting for some sort of bud to form...NOTHING!...yet very healthy growth on all...., quite luxuriant growth on some! :-(((

It's rained non-stop for 2 days...sick to death of it already! LOL. Hopefully tomorrow will be dry and I can take some photos. ...fingers crossed!