Phillips received a commission in the Bedfordshire and Hertfordshire Regiment early in the Second World War and was sent to Singapore with the 5th battalion of his regiment, a part of the 18th Infantry Division, arriving shortly before Singapore fell to the Japanese on 15 February 1942. From December of that year until April 1944, he worked as an intelligence officer on the Thailand-Burma Railway, in the jungle prison camp at Tarsao, collecting and disseminating information from the outside world, from local newspapers and hidden radios, in order to boost the morale of his fellow prisoners. In February 1945 he was interrogated by the "Kempeitai" (Japanese Military Police) and sentenced to two years’ imprisonment. He arrived at Singapore’s Outram Road Jail, known as “The Belsen of the East”, in July 1945 but was released after only a month. For his work during this time in Burma and Singapore he was awarded the MBE in 1946.