Ellis, 36, would be a backup to starter Austin Hedges if he makes the big league roster.
Ellis, known for his ability to call a game, spent most of his career with the Los Angeles Dodgers. He caught Clayton Kershaw's no-hitter on June 18, 2014, and was Kershaw's preferred catcher with the Dodgers.
The 10-year veteran was traded to the Philadelphia Phillies in August 2016.
Ellis is a career .237 hitter with 43 homers.