There are several synonyms for the phrase "do the right thing by". Some of the commonly used synonyms are "act fairly towards", "be just to", "show kindness to", "treat properly", and "serve honestly". All these synonyms refer to the concept of doing the right thing by someone or something. It means to act in a moral and ethical way towards others, to behave honestly, and to treat others with respect and fairness. Doing the right thing by someone implies a sense of responsibility and accountability in one's actions and decisions. Using different synonyms can add variety to the language and help express the same idea in different ways.