I recently adopted a 3-5 year old black miniature poodle?

The foster Mom told me that the dog had come from a puppy mill (the first year of his life) and had been used for breeding, and the puppy mill owner cut the dog's vocal cords. Now due to his vocal cords being cut, the dog gags and spits up a foamy phlegm, especially after he eats and drinks water. What could be the cause or the cure for this poor pup with a heart of gold?