The 68-year-old Montgomery returned to the team after surgery on May 19 and was active with the club throughout his treatment. He helped greet the Taney Dragons Little League team during a pregame ceremony Wednesday night.
Gillick led the Phillies to the 2008 World Series championship. He stepped down after that season and became a senior adviser to Montgomery and GM Ruben Amaro Jr.
Montgomery has been the team president since 1997. The team said Montgomery will return to his duties when he is fully recovered.