Falter was sent back to the team's alternate site Monday, Matt Gelb of The Athletic reports.
Falter got to make his major-league debut Sunday but had to do so at Coors Field. He gave up two runs on four hits in two innings of work. He could be back up when the Phillies need another lefty later in the season but will make way for Jose Alvarado, who returned from the COVID-19 injured list in a corresponding move.