The game at Citizens Bank Ballpark is scheduled for 3:40 p.m. Pacific time but will start at 3:10 instead, with rain in the forecast for later in the evening.
The Giants have Opening Day starter Logan Webb going in the second game of the series while the Phillies have their ace, lefty Cristopher Sánchez, on the mound; San Francisco earned a 6-0 win at Oracle Park the last time the team saw Sánchez.
The Giants dropped game one of the series 7-0 on Tuesday night, so would need to win Wednesday night and Thursday to earn their fourth consecutive series victory.
NBC Sports Bay Area and KNBR will adjust their schedules to accommodate the schedule change, with the pregame shows starting 30 minutes earlier.