That's such a sad story! I'm amazed that doctor associated your phlegm with GERD. I would have thought he would have given you decongestants or antibiotics. I'm so sorry you are going through this now.
My dad was never diagnosed with GERD, but when he was in the hospital for brain surgery last year, we discovered that among the other medicines they were giving him, was Protonix. At the time, I was on that myself and was shocked. He didn't have any problems with his stomach. They kept him on that for a few months and never told him to go off. When he went to his regular doctor, he finally asked him if he could stop. He has and thankfully, he never got rebound. Talk about
I don't have any good recommendations for coming off of the PPIs (I'm trying to do this myself) other than be careful what and how much you're eating.
As for the phlegm, I have chronic sinus problems too. I looked into alternative ways to treat my sinuses because sinus medicine made me nauseous and didn't help that much. I started using a Neti Pot. Have you ever heard of that? It's basically irrigating your sinuses with saline. You can do a Google search on it. It's amazing how it helped me! I feel like it's a miracle treatment. Now I just need to find the same thing for GERD
Hope you feel better soon!