FoxSports.com's Ken Rosenthal reported Phillips' pending absence on Thursday.
Rosenthal later tweeted that Phillips will have surgery on Friday, and would likely be out 8 to 12 weeks.
Phillips suffered the injury in the Reds' 4-1 victory over the Chicago Cubs Wednesday night when he made a diving attempt at a grounder and his glove got caught underneath him. The Reds originally called the injury a sprain.
A three-time All-Star and four-time Gold Glove-winner, Phillips has put up a slash line of .272/.308/.392 in 86 games this season.
Phillips's injury comes amidst a flurry of maladies for the Reds. In the same game Wednesday, rookie center fielder Billy Hamilton injured his left hamstring and was out of the lineup Thursday. In Thursday's game, starting pitcher Homer Bailey exited with a knee injury. On Tuesday, the team placed first baseman and former MVP Joey Votto on the 15-day disabled list with a strained left quad.
Earlier this season, catcher Devin Mesoraco and right fielder Jay Bruce spent time on the disabled list, and closer Aroldis Chapman began the year on the DL after being hit in the face with a ball in spring training.
The Reds entered Friday at 49-43, two-and-a-half games behind the first-place Milwaukee Brewers in the National League Central.
— Ben Estes