Phlebitis is a medical condition: a vein becomes inflamed — swollen, sore, and rough on the inside. A vein is a tube that carries blood back through the body. The place can look red and feel hot or tender, often in a leg or along a line where a drip went in. Though actually, doctors sometimes talk about thrombophlebitis, which is phlebitis plus a clot; the tidy word 'phlebitis' is the inflammation itself. It is hospital and clinic English, not casual chat, though a nurse may say it plainly to a patient. It is not an infection of the throat, and it is not about mucus, even though phleb- and phlegm look like cousins on the page. They are different Greek pieces.