The phrase "do one's duty" carries a sense of responsibility and obligation, but there are several synonyms that can be used to convey the same meaning. For example, one might use the phrase "carry out one's responsibilities" or "fulfil one's obligations" to express the idea that someone is doing what they are required to do. Additionally, the words "perform," "execute," or "accomplish" can be used to describe someone completing their duty. Other synonyms include "serve," "uphold," "behave responsibly," or "do what is expected." These terms all convey the importance of fulfilling one's duties, whether they be personal or professional in nature.