The phrase "He is my most beloved enemy" illustrates an oxymoron. An oxymoron is a figure of speech that combines two contradictory or opposing ideas, words, or phrases. In this case, "beloved" and "enemy" are two words with opposite meanings that are being used together in the same phrase. It creates a paradoxical situation where the speaker expresses affection or admiration towards someone who is supposed to be an adversary or opponent. The use of oxymoron in literature or rhetoric can create a powerful effect by highlighting the complexity of human emotions and experiences.