The phrase "fix up on" can be synonymous with several other terms depending on the context. For instance, it could imply "work on" or "revise" when referring to a written document or a draft. It could also mean "repair" or "fix" when referring to a broken object or equipment. Another possible synonym for "fix up on" could be "prepare" or "arrange," particularly when getting ready for a social event or a meeting. Moreover, the phrase could be used interchangeably with "improve" or "enhance," particularly when talking about skill development or achieving a goal. In any case, the context determines the most appropriate synonym for "fix up on".