Blanton is on the disabled list while recovering from an oblique strain in spring training.
Reading lost 5-2 to Harrisburg. Blanton gave up all five runs on a pair of homers.
Blanton said he feels good and ready to return to the Phillies' rotation. This was the third rehab start for the 29-year-old Blanton. He said he doesn't know when the Phillies will activate him from the disabled list.