I've had this problem quite a few years back. A doctor explained that when phlegm builds up in my throat and
does not go down, that fibers in my throat them push the phlegm upwards until I cough for re-swallow (a-hem).
He prescribed a medicine (sorry, I don't recall the name) that causes the fibers in the throat to go numb, which forces the phlegm to only go down. I used this medicine for about a week and
the problem was gone. This solution worked for me.