Phlegm is a slur used to describe Belgians in a derogatory way. Pronounced "flems", from Monty Python's Flying Circus.
The word Phlegm is a racial slur that has been used historically to degrade and dehumanize belgians. The word is still used by some people for this purpose, and it is seen as offensive and hurtful to belgians. If you are unsure about whether or not it is appropriate to use the word Phlegm, it is best to err on the side of caution and avoid using it in any situation.