If its the border perennial Phlox, you can take cuttings of emergent young shoots in spring or you can lift the plant in spring and take root cuttings. Not really good to do now though.

Can you split a clump, too, Fractal? I'm sure I've done that before......in early spring, I seem to remember.

Yes, you can though for some reason cuttings by root or shoot establish quicker.

You need to do them from root cuttings to avoid stem eel worm.

...if your plants are infected :-)

I don't think mine are - I sincerely hope I don't get to meet any of them! How do you recognise them, please?

They are slow acting usually, but the top most leaves on the plants gradually get narrower and narrower until they only have a midrib. Plants can live with the eel worms for a long time without showing any major symptoms.

Thanks, Ob. I'll watch out for it. I have a lot of Phlox plants...