Grass growing through ground cover plants - help!

I'm fairly new to gardening, but last year planted a selection of phlox in various colours. At the moment they are blooming beautifully and look gorgeous. However, I've got blades of grass growing through the plants. Is there any other way to deal with this, apart from painstakingly removing each blade one by one - although I can't get to the roots? I've recently planted more ground cover plants in another part of the garden, so may well be faced with the same problem. I'd be grateful for any advice.