Use up is a phrasal verb that means to consume or exhaust all of a particular thing or resource. Synonyms for use up can include words such as deplete, exhaust, consume, expend, drain, run out of, finish, utilize, and employ. These words can be used interchangeably with use up in situations where a limited amount of resources or energy is being consumed or utilized. For example, instead of saying "I used up all my energy," you could say "I depleted all my energy." These synonyms can add variety to your writing and help you avoid repeating the same phrasal verb multiple times.