The departure of the midfielder brings to a close a 12-year association with Leeds, whom he came through the academy system with, and helped steer back to the Premier League in the 2019-2020 campaign.
Phillips addressed the club and its supporters in a lengthy statement on social media shortly after the confirmation of his transfer, thanking them all and reserving additional praise for former boss Marcelo Bielsa.
The Argentine, who guided Leeds back to the top-flight before he was relieved of duties earlier this year, is widely credited with turning the midfielder into one of the sharpest talents in the English game.
“I would like to express how much of a privilege it has been to play for this amazing club,” Phillips stated. “Since making my debut at 17, it has been a journey any Leeds lad could wish for.
“When I was young, I went to see my first ever Leeds game at Elland Road and from that moment, I knew that my dream was to put on that white shirt and walk out on that pitch.
“I’d like to thank everyone involved at the club for making Leeds one of the best clubs on earth. Every manager I have played under for showing trust in me and teaching me all I know.
“I cannot mention Leeds without mentioning one special person – Marcelo. [You are] the best manager I have ever come across.
“He was a man that gave the club life, he gave the players, and everyone involved in the club belief that we were good enough to return to the Premier League.”
Phillips’ arrival at the Etihad Stadium came on the same day that Gabriel Jesus completed a £45million switch to Arsenal.
Leeds also confirmed on Monday that 18-year-old midfielder Darko Gyabi has joined the club from City for an undisclosed fee in a separate deal to the one involving Phillips.
The youngster played 10 times for City’s Under-23 side last season and has been capped 12 times by England at youth level.
Gyabi becomes Leeds’ fourth signing of the window, following the arrivals of Brenden Aaronson, Rasmus Kristensen and Marc Roca.