Phillips joined the CIA as a part-time agent in 1950 in Chile, where he owned and edited "The South Pacific Mail", an English-language newspaper that circulated throughout South America and several islands in the Pacific. He became a full-time operative in 1954, and operated a major psychological warfare campaign in Guatemala during the US coup and its aftermath. He rose through the ranks to intelligence officer, chief of station and eventually chief of Western hemisphere operations, serving primarily in Latin America, including Cuba, Mexico, and the Dominican Republic. Phillips retired from the agency in 1975 and founded the Association of Former Intelligence Officers in the same year.