Antonyms for the phrase "mixed it up" are terms such as organized, separated, arranged, and systematized. These antonyms describe actions that bring order and structure to a situation or environment, as opposed to the notion of mixing things randomly or haphazardly. An example of an antonym for "mixed it up" might be "sorted it out," which implies taking the time to separate and categorize things in a thoughtful and methodical way. Other antonyms might include "tidied up," "put in order," or "categorized," all of which suggest a deliberate effort to bring clarity and order to a situation.