The Asian champion beat strong rivals to win the women junior individual 2,000m event with a time of 10min 31.094sec.
Svetlana Ussova of Kazakhstan came second with 10:35.802, and Vietnam’s Nguyen Thi Tuyet was third, timing 10:42.825.
This was Phuong’s second gold at the tournament. Earlier, she won the women junior doubles 200m category.
On June 8, the 18-year-old also pocketed one silver and two bronze medals. She grabbed a silver in the women junior doubles 500m event, along with Tuyet. The pair took 2:02.875 to complete their race.
Chinese duo Huan Men and Qi Li, who lost to the Vietnamese girls in the 200m pool, took the title, clocking 2:01.775. Ussova and her teammate Alexsandra Kim came third at 2:05.206.
Phuong won bronzes in the women junior individual 200m and 500m disciplines.
Nguyen Thi Ngan and Tran Thi Lan also won Vietnam another bronze in the women doubles 500m event. Anne-Sophie Lavoie-Parent and Rowan Hardy-Kavanagh of Canada took the title, while their teammates Hannah Macintosh and Nadya Crossman-Serb pocketed silver.
Vietnam completed the Szeged competition with two gold, two silver and four bronze medals.