The phrase "is supreme" often refers to something that is the ultimate or highest authority. There are many synonyms for this phrase including "is paramount," "is dominant," "is sovereign," and "is preeminent." "Is paramount" emphasizes the importance or significance of something, while "is dominant" suggests something that is powerful and influential. "Is sovereign" implies an absolute, uncontested authority. Lastly, "is preeminent" connotes something that is superior or outstanding in comparison to others. These synonyms can be used interchangeably depending on the context and the level of emphasis needed. All in all, these synonyms highlight the essence of something that is supreme, dominant, and unrivaled.