The phrase "serve time" is commonly used to refer to the amount of time a person spends in jail or prison. However, there are several synonyms that can be used interchangeably with this phrase. Some examples include "do time," "serve a sentence," "incarcerate," "confinement," "detain," and "imprisonment." Each of these terms carries a slightly different connotation, but all refer to the act of being confined against one's will for a certain period of time. It's important to note that the use of these synonyms can help avoid repetition in writing or speech, while still conveying the same general meaning.