That behavior no matter the cause releases endorphins. So at some point it no longer is about what first triggered the chewing but about the endorphins being released. This happens even if the chewing is making things worse.
Finding something else for the dog to chew is probably the simplest solution. Which means making it so the dog can’t worry at its paw. Look for a medical boot designed to keep the dog from licking or chewing his paw. Then find a variety of chew toys for the dog.
He has chew toys but may work on them for a few minutes. Chew bones gives him the runs unfortunately.