Antonyms for the phrase "being a matter of" include "not relevant," "irrelevant," "unchangeable," and "incalculable." When something is not relevant, it means that it's not important or significant. If something is irrelevant, it does not relate to the situation at hand or has no bearing on the matter. Unchangeable suggests that something cannot be altered or modified, while incalculable implies that something is too complex to be accurately estimated or predicted. Knowing antonyms to "being a matter of" can help in expressing the opposite meaning or perspective regarding a particular issue or topic.