Anxiety used to significantly increase my GERD symptoms. It was a terrible circle, GERD would cause anxiety, which in turn increased my symptoms. Then when I would have a rough day at work, everything would be intensified further and I'd basically be non functional.
Interestingly enough, the thing that did the most for my anxiety and also my GERD symptoms (over PPIs, Gaviscon, and all of the other stuff you can try) was an anxiety medication, Klonopin. Unfortunately, it was not sustainable at all. I developed a tolerance to the medication and needed to increase my dose, then I became tolerant to that. My doctor upped the dose a second time and it wasn't long until I was tolerant of that and felt no benefits, other than knowing if I missed a pill, I'd feel awful. I didn't want to keep increasing the dose and did not like the fact I was basically hooked on it, so I slowly weened off of it, which was pretty rough.
I also tried Cymbalta and then Lexapro, completely because of my GERD related anxiety. I felt neither benefits nor side effects. Couldn't tell a difference, so I stopped taking it. I do have friends who have taken both and have had huge successes controlling anxiety.
So, bottom line, anxiety and stress can definitely increase GERD symptoms.