Sounds like a Spittle Bug. My experience is that they are an occasional visitor to the garden, and while technically harming your plants, their populations are such that they are not a problem.

If concerned, just apply some medium-pressure water from a hose.

I get lots of them in my garden this time of year. They are really gross. Like aphids, they suck juices from your plants. In small numbers they aren't much to worry about, but if you have a lot they can be disease vectors and deform flowers. Hosing them off works somewhat; pushing aside the spittle and finding and squishing the little bugger works even better, but I recommend wearing gloves.

Spittle bugs. Just go in with your fingers and pinch the green bugs from the center of the spit.

They love my phlox and my dianthus as well. I just squish em' too!!

I just use a spray bottle with a very mild detergent solution, and it does the trick. They really don't seem to harm my plants.