Thompson was optioned to Triple-A Lehigh Valley on Saturday, Matt Breen of The Philadelphia Inquirer reports.
The 24-year-old's season got off to a rough start, as he allowed four runs on six hits in his season debut on March 31. He collected the save Saturday against the Marlins, though, logging three innings of shutout ball to finish out the Phillies' 20-1 shellacking of the Marlins. Thompson isn't available to pitch for a few days now, however, making him an obvious candidate to demote to make room for Sunday starter Jake Arrieta on the active roster. Thompson should work as a starter in the minors, but he might return to the Phillies bullpen soon if help is needed once again.