Armstrong will serve as the Rays' starting pitcher for Thursday's game against the Phillies, Kristie Ackert of the Tampa Bay Times reports.
The Rays haven't officially confirmed that Armstrong will be operating as an opener, but considering that he hasn't covered more than two innings in any of his 19 appearances in the majors or minors this season, he's unlikely to work more than once through the Phillies batting order. Tampa Bay doesn't have an obvious pitcher available to work in bulk relief behind Armstrong, so the Rays could treat Thursday's series finale as more of a bullpen day.