Garrett will start Game 2 of Sunday's doubleheader against the Phillies, Joe Frisaro of MLB.com reports.
The young left-hander was recalled earlier in the day to serve as the 29th man for the twin bill, and he'll receive the starting nod in the nightcap. Garrett made his major-league debut last week and earned the win after allowing one run on three hits with six strikeouts and two walks over five innings.