Sweeney, who had driven in the first run of Oakland's 5-0 victory with a double, sprained his left ankle while scoring on a single to center field by Jack Cust.
Phillies catcher Carlos Ruiz blocked the plate with his foot while awaiting Shane Victorino's throw, and after Sweeney's foot clipped that of Ruiz, he slid past the plate before reaching back with his left hand to elude Ruiz's tag.
Sweeney, who entered Thursday with the highest batting average (.286) among Oakland's regulars, stayed in the game and played defense in the second inning, but was replaced by Rajai Davis when the A's took the field for the top of the third. Davis took over in center field, with starting center fielder Carlos Gonzalez moving to right.
"It swelled up pretty quick," Oakland manager Bob Geren said of Sweeney's ankle.
Head athletic trainer Steve Sayles said late Thursday afternoon that Sweeney was sent for X-rays, but Sayles had not yet gotten a report.
The A's, who tied an Oakland record by using the disabled list 22 times last season, have used it 15 times in 2008 and currently have four players sidelined: designated hitter Frank Thomas, first baseman Mike Sweeney, right-handed reliever Joey Devine and outfielder Chris Denorfia.
Mychael Urban is a national writer for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.