Phu was a company commanding officer in the 5th Battalion of Vietnamese Paratroopers (5th BPVN, standing for Bataillon de Parachutistes Vietnamiens in French) of the Vietnam National Army during the battle of Dien Bien Phu. He was captured with the remainder of the French garrison when it surrendered to the Viet Minh on 7 May 1954. In the Army of the Republic of Vietnam, Pham served as Chief of Staff of the Special Forces, commander of the 1st Infantry Division, and director Quang Trung Training Center, before taking the command of the II Corps/Military Region II in Pleiku.
He was the commander during the battle of Ban Me Thuot which was part of North Vietnam's Campaign 275 to capture the Central Highlands following the victory at Phước Long on 6 January 1975. His troops suffered heavy losses on the way of withdrawal to the coastal areas in April 1975. He committed suicide in Saigon on 30 April 1975, the day of the fall of Saigon when the Republic of Vietnam fell to the forces of the North Vietnamese Army.