Phillies Top 30 Prospects No. 25: Lanky Left-Hander Mavis Graves

This is the sixth in a series of stories breaking down the Philadelphia Phillies’ Top 30 prospects heading into 2026.

Selected out of high school in the sixth round of the 2022 MLB Entry Draft, left-hander Mavis Graves signed with the Phillies for $247,500, taking him on as a project for less than the slot value. The 6-foot-6 22-year-old has navigated ups and downs to this point in his professional career, struggling to a 7.68 ERA in rookie ball during the 2023 season.

He rebounded to mow through Single-A Clearwater, fanning 117 batters in 84 innings, then endured a rough start to High-A with Jersey Shore in 2025. Graves posted a 1.94 ERA over the final two months of the season with the BlueClaws, however, making him a solid bet to advance into Double-A in 2026 — for a developmental high school pick, it’s hard to do much better than that.

His four-seam fastball clocks slower than one might expect for a pitcher of his height, averaging in the low 90s, but Graves can dial it up as high as 95 mph.

Best in the Bullpen?

Graves compliments the four-seamer with a two-seamer, a 55-grade slider and a cutter. After barely using his changeup during his first two professional seasons, Graves developed it into a legitimate offering in 2025; he also has a sweeper that can miss bats. Given the spotty fastball velocity, Graves might project best as a reliever tasked with going all out for an inning or two.

His reliance on the breaking balls could also make it difficult for him to navigate more than one or two turns through the order, and he averaged less than four innings per game in High-A, never managing to finish the sixth. Baseball Savant rates Graves’ control as a below average 45-grade; he averaged 11.35 strikeouts and 5.62 walks per nine innings last season, and batters will grow more discerning as he advances through the system. Graves can improve too, though, and in this data-focused era of tracking spin patterns and throwing mechanics, offseason overhauls are well within the realm of possibility.