When it comes to the opposite of the phrase "be in authority," there are a few different options. One antonym could simply be "lack authority," indicating a complete absence of power or control. Another option could be "be subordinate," which means to be under someone else's authority or control. "Be powerless" could also work as an antonym, suggesting that there is no ability to control or direct others. Lastly, "be a follower" or "be subservient" could work as antonyms, suggesting that one is willingly following or obeying someone else's authority rather than being in control themselves.