After starting the 2021 season at the Phillies' alternate training site, Vierling was assigned to the Double-AReading Fightin Phils to begin the minor league season. He was promoted to the Class AAA Lehigh Valley IronPigs after hitting .345 with 6 home runs and 16 RBIs in 24 games with Reading.[14]
Philadelphia Phillies (2021–2022)
On June 19, 2021, Vierling was selected to the 40-man roster and promoted to the major leagues for the first time.[15] He made his Major League debut that day as a pinch hitter, hitting a single to right field in his first at-bat off of San Francisco Giants reliever Jarlin García while also stealing second base and scoring a run.[16] He hit his first Major League home run on September 25, 2021, in Philadelphia in a 3–0 win over the Pittsburgh Pirates.[17] In 2021, he had the fastest sprint speed of all major league first basemen, at 29.2 feet/second.[18] By the first anniversary of his MLB debut, Vierling had started a game at six positions (1B, 2B, 3B, LF, CF, and RF).
On June 7, 2022, he was recalled to the Phillies from AAA affiliate, Lehigh Valley Iron Pigs, and hit the game-winning home run off of Josh Hader.[19] Vierling's first multi home run game was on June 17, 2022, in a win against the Washington Nationals.[20] On September 21, 2022, Vierling went 5-for-5, including his first walk-off hit in the 10th inning, in a 4–3 win against the Toronto Blue Jays, halting a five-game losing streak.
In the 2022 regular season, he batted .246/.297/.351 in 325 at bats, with six home runs, 32 RBIs, and seven steals.[21] He had the fastest sprint speed of all Phillies players, at 29.6 feet/second.[22] He played 61 games in center field, 37 in right field, 30 in left field, four at second base, and two at first base.[21] As a center fielder, he set up farther away from home plate than any other major leaguer, at a depth of 332 feet.[23]
Vierling played in 12 games during the Phillies playoff run to the World Series in 2022. He had 15 plate appearances, with two hits, one walk, one RBI, and two runs.[24][25]