[5] In 2016, Phillips left Bolton Wanderers' academy and trained at Huddersfield Town after he secured a scholarship at the University of North Carolina at Charlotte.

[13] On 27 December 2019, Liverpool announced that Phillips would be recalled from his loan on 1 January 2020 due to a defender injury crisis at his parent club.

[14] Twelve days later, after making his first team debut for Liverpool on 5 January 2020 in an FA Cup third round match against Everton, he was loaned back to VfB Stuttgart for the remainder of the 2019–20 season.

[17][18] On 10 March 2021, Phillips made his Champions League debut, putting in a man of the match performance in a 2–0 win over RB Leipzig, and helping Liverpool advance to the quarter finals 4–0 on aggregate.

[22] With game time limited in the 2021–22 season, Phillips admitted to being ready to leave the club in the January transfer window.

[24] Regarding the move, Klopp commented that "he would have loved to have kept him [at Liverpool]" and that Phillips was "incredibly reliable [and a] great figure here at the training ground.

[33] Derby head coach Paul Warne stated that his signing would give him "greater tactical flexibility" in team selection.