The Phillies won their fifth consecutive National League East championship, and also finished with the best record in baseball for the second straight year.

The offseason for the Phillies began on October 23, 2010, when they lost the National League Championship Series to the San Francisco Giants.

[5] On December 15, the Phillies re-signed Cliff Lee, the starting pitcher whom they had traded to the Seattle Mariners during the previous offseason in order to acquire Roy Halladay.

The Mets' Daniel Murphy was batting as a pinch-hitter against Phillies' reliever Ryan Madson when the fans started chanting "U-S-A!

"[9][10] Later, it was determined that the chants were in response to the news that al-Qaeda leader Osama bin Laden, the mastermind of the September 11 attacks, had been killed by United States special operations forces in Abbottabad, Pakistan.

In the middle of the month, they went on a seven-game winning streak, taking three of four from the Chicago Cubs, and a four-game sweep of the Florida Marlins.

The Phillies sent five players (Roy Halladay, Cliff Lee, Cole Hamels, Plácido Polanco, and Shane Victorino) to the All Star Game.

The Phillies began August riding a nine-game winning streak, and in time, extended their lead in the NL East to 8.5 games.

After several months of being injured, Roy Oswalt came back into action in the Phillies, winning his first two starts by a combined score of 16–3.

The Phillies also led the major leagues in attendance for the first time, with 3,680,718 fans (a franchise record), an average of 45,440 per game.

Game 1 saw the Cardinals jump out to an early lead, with a three-run homer by Lance Berkman in the top of the 1st, off Phillies ace Roy Halladay.

Game 2 featured another Philadelphia ace, Cliff Lee, facing the Cardinals' Chris Carpenter, who would make his first start on three days rest of his career.

The Cardinals were able to fight back and get 2 runs, but Ryan Madson shut the door, with a 5-out save, to give the Phillies a 2–1 series lead.

Game 5 featured a marquee pitching matchup, with former Toronto teammates, Roy Halladay and Chris Carpenter facing off.

First baseman Ryan Howard suffered a torn Achilles tendon, that would forced him to miss some time for the 2012 season.

Jimmy Rollins (shortstop) and Roy Halladay (one of three starting pitchers) were named to the MLB Insiders Club Magazine All-Postseason Team.