Thanks for posting this. This is why I recommend going along with diagnostic testing recommended by a veterinarian that has examined your dog, rather than looking for answers on the internet.
Excerpt below from: http://www.companimalmed.com/article/S1938-9736(15)00005-7/abstract
Phenobarbital-responsive sialadenosis (PRS) is a rare idiopathic disease in dogs. Vomiting, retching, and gulping with bilateral enlargement of the submandibular salivary glands are the more frequent clinical signs. A thorough diagnostic examination must be performed to rule out the most important systemic etiologies involved with chronic vomiting, as there is no specific test to diagnose PRS. Diagnosis is confirmed clinically by a rapid and dramatic improvement of clinical signs after instauration of phenobarbital treatment.
