I, too, have problems with phlegm, and recently discovered that there are two types of acid reflux. I dont have heartburn, but I don't have lots of phlegm in my throat in the morning.
The following is a summation from AI. I hope it helps you!
Acid reflux, particularly Laryngopharyngeal Reflux (LPR) or "silent reflux," causes excess phlegm, throat clearing, and a "lump in the throat" sensation when stomach acid irritates the throat and larynx. The body produces this mucus to protect tissues from acid damage. Key remedies include elevating your bed, avoiding late-night meals, and reducing caffeine/fatty foods.