Phong served as the commander of I Corps, which oversaw the northernmost part of the country, from 20 May to 30 May 1966, when he was replaced by Lieutenant General Hoàng Xuân Lãm. He was one of five different I Corps commanders in two months,[1] as Prime Minister Nguyễn Cao Kỳ struggled to find a leader of whom he approved while the Buddhist Uprising was taking place.[2]: 138
He was killed on 1 December 1972 when the Republic of Vietnam Air Force plane he was travelling on crashed in bad weather on approach to Tuy Hoa Air Base. Four other South Vietnamese and two USAID officials were also killed in the crash.[3]