Mucus is typically a thin, slippery fluid that goes mostly unnoticed unless production increases due to illnesses or allergies. Typically, a person does not need to cough up mucus, as they can clear it out when they blow their nose or use saline sprays or solutions.
Phlegm is a thicker, more viscous mucus in the lungs and airways. It is the type of mucus a person coughs up. Phlegm is often the body’s response to irritation or an infection and can range in color depending on the cause.