[3][4] After signing, Phillips was assigned to the AZL Rangers of the Rookie-level Arizona League to make his professional debut; in 15 innings pitched for them, he posted a 0–1 record with a 3.60 ERA.

[18] Phillips was designated for assignment on July 17, 2021, after struggling to a 1–5 record and 6.75 ERA in 10 games between Frisco and the Triple-A Round Rock Express.

[21] He was placed on the injured list on September 13 due to a right elbow impingement suffered while he was with the High–A Jersey Shore Blue Claws, ending his season.

[21] For the start of the 2023 season, Phillips was assigned to Reading, before being promoted to the Triple–A Lehigh Valley Iron Pigs on July 26.

[25][26] In his debut, Phillips tossed four innings of relief, striking out seven batters and allowing one run in a 6–0 loss to the Atlanta Braves.

Due to injuries to starters Taijuan Walker and Spencer Turnbull, Phillips was added to the starting rotation.

5 starter, Phillips surrendered six runs on eight hits in only 0.2 innings of work against the Toronto Blue Jays; despite this, the Phillies came back to win the game, 10–9.