Spitting everywhere is uncivilized, because sputum contains many germs, such as bacteria and viruses.
Phlegm is the secretion of respiratory tract. Patients with respiratory diseases only secrete a lot of sputum when they are infected by foreign pathogens. Sputum contains a variety of virosomes, which are easy to spread through droplets and infect healthy people.
Phlegm is the secretion of respiratory tract, and healthy people generally have no sputum. However, if you have respiratory diseases, you will produce a lot of sputum after being infected by pathogenic microorganisms.