By right of office is a phrase often used to refer to someone's authority or power derived from their position or designation. However, there are several synonymous phrases that can be used in its place. One such phrase is "by virtue of their position," which means the same thing, indicating that someone has the authority or power due to their position or role. Another phrase that can be used is "in their official capacity," indicating that someone's actions are carried out in the capacity of their role or position. Additionally, other synonymous phrases include "due to their station," "as a result of their role," or "through their designation".