When it comes to finding synonyms for the phrase "most underemployed," there are several options to consider. Some possible alternatives might include "worst employed," "least utilized," "poorly utilized," or "underutilized." Each of these phrases captures the essence of the idea that someone is not fully using their skills, experience, or education in their current job. Other possible synonyms could include "unfulfilled," "undervalued," "mismatched," or "stagnant." Ultimately, the most appropriate synonym will depend on the specific context in which it is being used, but these options offer a starting point for finding a suitable replacement.