The antonyms for the phrase "is one's back" can be terms like - be on one's side, support, aid, ally, cooperate, collaborate, or assist. These words signify a positive relationship, where people are standing by your side and helping you out. Whereas, "is one's back" often represents a negative connotation which signifies someone's opposition, betrayal, or lack of support for you. It's essential to understand that not everyone in life will have your back, but you can always find people who will stand by your side and be your advocates. By creating and nurturing positive relationships, you can surround yourself with people who will help you grow and achieve success.