Ordinary milk helps line the throat, too.
There is also a chance his thyroid has swollen
up, which that gland
wraps around the trachea just above where the collar bones meet, so he can feel of it there and see if it's swollen, and if so, an endocrinologist can check it out and see if that is working like it should. In rare instances, could be a possible neurological disorder that is affecting his ability to swallow... the endocrinologist, if he doesn't find anything, can refer him to one.