Coming into DLSU, Montalbo was seen as their next big recruit since Jeron Teng. He started getting minutes after Torres was out with an illness. That season, the
De La Salle Green Archers won the championship over the
UST Growling Tigers. In 2014, Montalbo and Subido participated in the Nike All-Asia Basketball Camp, where they both made the Top 20 Asian Players list. In
Season 77, he stepped up once again as Torres was out with another injury, and took the starting role. In a win over the
Adamson Soaring Falcons, he had a college career-high 18 points. In a win over the Tigers, he pulled a calf muscle, which took him out of the rotation for a week. That season, the Archers made the Final Four, but were defeated by the
FEU Tamaraws. In 2015, during a
Filoil Flying V Preseason Cup match against the
UE Red Warriors, Montalbo suffered an ACL injury. Without him, the Archers didn't make the Final Four in
Season 78. He used the time away from basketball to recover and focus on his studies, making the
dean's list for his course in business management. He made his return to the team during the 2016 Filoil Cup. In a
Season 79 win over Adamson, he 12 points, eight rebounds, six assists, and three steals. That performance led to him earning a Player of the Week award, becoming the third Archer that season to win one after
Ben Mbala and Teng. Later in the tournament, he hit a clutch triple against Adamson that gave La Salle their eighth straight win. Their win streak ended at 12 games with a loss to their archrivals the
Ateneo Blue Eagles. In their last game of the elimination round, he scored 13 points in a win over FEU, and the Archers finished first in the standings with a record of 13–1. He finished the elimination rounds third in minutes per game on the team. They went on to sweep Ateneo in the finals. That season, he led the league with career-highs of 2.8 steals and 2.8 assists. This was his second UAAP championship. He was awarded the Pivotal Player Award during the
2017 Collegiate Basketball Awards. In the preseason, Montalbo was involved in a bench-clearing brawl against FEU. Despite being punched in the face by a FEU player, he had no injuries. For
Season 80, he was made team captain. They got their first win of the season against FEU, in which he made three straight threes, and finished with 12 points, four rebounds, three assists, and two steals. He was able to contribute that game despite coming off a viral infection that had him hospitalized. In a loss to Ateneo, he committed a costly turnover in the last nine seconds of the game that allowed Ateneo's
Matt Nieto to get the win at the free throw line. He then scored 12 points in a win over the UP Fighting Maroons that secured La Salle into second place. In a rematch against Ateneo, he hit a clutch floater that gave La Salle the win. In the Final Four, he guarded Adamson's best scorer in
Jerrick Ahanmisi, limiting his scoring. The Archers made the finals once again, where they lost Game 1 in the best-of-three series. He rallied the Archers in Game 2 while contributing nine points, five assists and three steals, and they tied the series. The Archers however, lost in Game 3 and the Eagles reclaimed the championship. Three games into
Season 81, Montalbo fractured his left thumb, and expectations were that he would be out four to six weeks. However, against his doctors or his parents' advice, he played again after two weeks. He made his return in a loss to Ateneo. Montalbo reasoned that he made the risk of returning as it was his final season and that he would continue playing. His college career ended in a loss to FEU as they did not qualify for the postseason. He graduated with a degree in business management in 2021. == Amateur career ==