I have heard that a chronic cough sets up a chronic irritative bronchitis that means that the more you cough, the more you will need to later-- the phlegm comes to soothe the irritation caused by the cough.

First thing would be see a doc about the cough--

But what I have done to stop the cycle when I see it occurring is do the coughing that is productive maybe twice a day to clear out the crud, then use a cough suppressant to keep me from that reactive coughing that is NOT productive and that keeps the irritation going, producing more crud.

Make sense?

So on gig day you could try doing your coughing that afternoon, and try hard NOT to during the gig.

Alice (I think) has written a lot about the singing voice; maybe dry vocal cords are part of the problem, and the phlegm is coming to coat them? Maybe the coating is too thick and you need to drink a LOT more water in the day?

~S~