I get phlegm and cough when I laugh a lot. Why does this happen?

Chronic cough. I don't know why you have a chronic cough, but the cause of that is the cause of the phlegm. The most common causes of chronic cough (asthma, reflux, drugs) don't usually produce phlegm, but allergies with post nasal drip may. See your physician this week to see what is behind your cough.