The Phillies released Castillo on Aug. 12.
Castillo logged a 4.43 ERA over 20.1 innings at the big-league level with the Royals in 2023, but he didn't make any appearances for the Phillies in 2024 after being added to the organization's 40-man roster over the offseason. The right-hander was outrighted off the roster earlier this month and was eventually cut loose after compiling a 7.62 ERA over 52 innings this season between Triple-A Lehigh Valley and Double-A Reading.