What causes people to spit up white phlegm?

Bronchitis can cause a person to spit up white phlegm, according to Cedars-Sinai Hospital. This typically means that the bronchitis is viral in nature.

Other symptoms include a fever, a runny nose and a cough. Chest discomfort and fatigue are also typically present. If the phlegm is green or yellow, this is more indicative of bacterial bronchitis. When a person experiences a cough with or without phlegm for more than 3 weeks, they should contact a doctor, as stated by Mayo Clinic. This is also true if they cough up blood. Only a doctor can diagnose bronchitis and determine the treatment options that are available.