Philadelphia, PA -- (Sports Network) - The Philadelphia Phillies bolstered a thin starting rotation on Thursday, acquiring pitcher Joe Blanton from the Oakland Athletics for three minor league prospects.

The Phillies sent infielder Adrian Cardenas, outfielder Matt Spencer and pitcher Josh Outman to Oakland in exchange for Blanton.

Blanton, a first-round pick by the A's in the 2002 draft, has struggled to a 5-12 record with a 4.96 earned run average in 20 starts this season. However, the right-hander was 14-10 with a 3.95 ERA last season while eating up 230 innings for Oakland.

For his career, Blanton is 47-46 with a 4.25 ERA in 122 outings -- 118 starts -- over five major league seasons.

"We've been attempting to upgrade our rotation and we feel like we've done that," said Phillies assistant general manager Mike Arbuckle. "We think Joe is a very strong, competitive pitcher that has the mental makeup to pitch productively in a pennant race. He pitches a lot of innings and takes some burden off the bullpen."

Blanton provides depth for a Phillies starting staff with several inconsistent arms. Brett Myers was optioned to Triple-A Lehigh Valley earlier this month after posting a 3-9 record with a 5.84 ERA in 17 starts, while Adam Eaton's future in the rotation is in doubt after allowing 16 runs -- 14 earned -- on 17 hits in 6 1/3 innings over his last two starts.

Cardenas is hitting .309 with four home runs and 23 runs batted in at Single-A Clearwater, while Spencer is hitting .249 with six homers and 41 RBI at Philadelphia's high-A affiliate. Outman, a lefty, is 5-4 with a 3.20 ERA pitching mostly in relief at Double-A Reading.