Falter made his MLB debut with the Phillies in 2021, and he spent the next three seasons alternating between Philadelphia and the Triple-A Lehigh Valley IronPigs, serving as both a starting pitcher and a reliever.

[1] He became interested in baseball when his father Darwin encouraged him to do a school project on Sandy Koufax, a pitcher whom Falter then sought to emulate.

[4] As a sophomore with the Chino Hills Huskies in 2013, Falter pitched a no-hitter, striking out 16 batters in an 11–0 victory over Bloomington High School.

[5] In his final season with Chino Hills, Falter had a 6–2 win–loss record, a 1.20 earned run average (ERA), and he struck out 97 hitters in 75+2⁄3 innings pitched.

[8] Although his pitch velocity was not overpowering, Falter displayed good command in the Gulf Coast League,[8] and he was 1–2 with a 3.45 ERA in his first season of professional baseball, striking out 25 batters in 28+2⁄3 innings.

[14] In 21 South Atlantic League starts that season, Falter went 8–7 with a 2.99 ERA, striking out 105 batters in 114+1⁄3 innings and impressing director of player development Joe Jordan.

[9] When the 2020 Minor League Baseball season was cancelled due to the effects of the COVID-19 pandemic, Falter was not assigned to the Phillies' alternate training site.

[26] He was recalled back to Philadelphia on June 15, where he served as the team's long reliever behind starters Spencer Howard and Vince Velasquez.

[27][28] He missed most of July with two separate stints on the COVID-19 injured list: once as a close contact of Alec Bohm, and again when he tested positive for the COVID-19 virus.

[9] Despite making the Phillies' 2022 Opening Day roster out of spring training as a reliever, Falter was sent down to Lehigh Valley at the end of April so that he could be stretched out into a starting pitcher.

[32] Falter never found a consistent role in Philadelphia or Lehigh Valley during the 2022 season: between April 26 and September 17, he was called up to the majors seven different times, filling in for injured starters Zach Eflin and Zack Wheeler, before being sent back to the IronPigs.

[9] The Phillies reached the MLB playoffs for the first time since 2011,[35] and Falter made his postseason debut when he started Game 4 of the 2022 National League Championship Series against the San Diego Padres.

[36] His outing lasted only 24 pitches, as he allowed four runs before being relieved in the first inning, but the Phillies came back to win the game and ultimately take the series.

[38] When top pitching prospect Andrew Painter suffered an elbow injury during spring training, Falter was named to the Phillies' 2023 Opening Day starting rotation in his place.

[31] Despite posting a 7.88 ERA and allowing a team-worst six home runs in spring training, the Pirates named Falter their fifth starter for the 2024 season.

[47] After a strong showing in the first two months of the season, during which he posted a 3.22 ERA and consistently went deep into games, Falter struggled with fatigue in June, which affected his performance.