The Seattle Mariners selected Phillips with the 64th overall selection of the 2020 Major League Baseball draft.[5] He signed for $1.1 million.[6][7] He made his professional debut in 2021 with the Modesto Nuts and was promoted to the Everett AquaSox at the season's end.[8] Over 17 starts between the two clubs, he went 7–4 with a 4.62 ERA, 111 strikeouts, and 46 walks over 76 innings.[9]
Phillips returned to Chattanooga to open the 2023 season.[14] In late June, Phillips was promoted to the Louisville Bats.[15] In 25 games (24 starts) between the two affiliates, he logged a cumulative 4–5 record and 3.86 ERA with 154 strikeouts in 105.0 innings of work. On September 2, 2023, Phillips was selected to the 40-man roster and promoted to the major leagues for the first time after Brandon Williamson was placed on the COVID-19 injured list.[16] In 5 starts during his rookie campaign, he struggled to a 6.97 ERA with 26 strikeouts across 20+2⁄3 innings pitched.
Phillips was optioned to Triple–A Louisville to begin the 2024 season.[17]