The term mucus may sometimes be used instead of sputum, but sputum refers to that mucus specifically secreted in the respiratory tract, whereas mucus may also be produced in the gastrointestinal tract, urological tract, and genital tract.
Phlegm is a type of mucus made in your chest.
You typically don't produce noticeable amounts of phlegm unless you are sick with a cold or have some other underlying medical issue. When you cough up phlegm, it's called sputum.
You may notice different colored sputum and wonder what the colors mean.
Yellow phlegm is a sign that your body is fighting off a mild infection.
"White blood cells are responsible for fighting infections, and as they get picked up in the mucus, they can cause it to have a yellowish hue,.
Green phlegm is an indication that your body is fighting off a more serious infection.