The phrase "on one's side" is commonly used to describe someone's loyalty or support towards a certain person or idea. Some synonyms for this phrase include "behind," "with," "in favor of," "supporting," "favoring," and "backing." These words all convey the sense of being on someone's side or supporting them in some way. Moreover, they indicate a sense of solidarity and shared goals or beliefs. When someone is on your side, you can count on them to be there for you and to help you achieve your objectives. Whether it's in a personal or professional setting, having people on your side is crucial to success.