There are several synonyms for the phrase "in a rage" that can be used to describe someone who is extremely angry or furious. Some of these synonyms include "enraged," "incensed," "fuming," "livid," "seething," and "infuriated." These words all convey a sense of overwhelming anger and show that the person is truly upset. "Enraged" and "incensed" are particularly strong synonyms, emphasizing the intensity of the person's emotions. "Fuming" and "seething" suggest an internal turmoil that is about to boil over, while "livid" and "infuriated" show a more outward display of anger. No matter which synonym is used, it is clear that the person is in a state of extreme displeasure.