"Foam" is another way of saying little bubbles and to "wipe" something means to clean it. I would guess they're referring to foamy saliva or spit coming out of the person's mouth. Also, a "fleck" is a very small piece of something.

It means to clean/remove (wipe) bits/little pieces (flecks) of bubbles (foam, those bubbles that liquids make, like bear or cleaning products) from your lips. I hope it's clear now, if it's not, let me know and I'll explain again.