Many people get bronchitis each year. When this happens, the bronchi become inflamed and mucus then builds up. As a person progresses through bronchitis, the goal is to loosen up phlegm and ensure the viability of it moving. This lets you cough it out of the body and speed up the healing process.
Spicy food. Specifically foods with high levels of chilies and cayenne pepper are a great choice. These foods will thin mucus that is gathering in the lungs, making it easier to cough out. Some spicy salsa can go with almost anything and does the job.