When I needed to do some speaking while my cough was bad, my doc gave me a prescription cough suppressant to use and it worked for 6 hours. I have also used it infrequently when I need to interact with the public and coughing would be problematic (working an informational booth where I talked for 4 hours.) But you need to try it first - it made my mouth slightly dry.
I always doubled up on airway clearance the next day to make sure nothing bad stayed in my lungs.
Sue