Answer:
The phrase "Let go" is a Euphemism
Explanation:
Euphemism means a mild or indirect word or expression substituted for one considered to be too harsh or blunt when referring to something unpleasant or embarrassing.For example, For example, “kick the bucket” is a euphemism that describes the death of a person and also as the question says, using "let go" instead of saying fired are examples of euphemism.