What Causes Choking On Food And Fluids Along With Spitting Up Of Phlegm?

Hi. My boyfriend went to take a bit of food and said that it must have went down the wrong pipe, as it made him choke. Well, now he says he still feels a strange pressure, like something may be stuck in his throat. When he tried to swallow fluid, he immediately coughs it back up. Since the incident, he has been spitting up a lot of phlegm. What do you think is happening here?