Phillips joined City in July 2022 from Leeds United, having excelled for the Elland Road outfit over eight seasons.
Before arriving at the CFA, he had also been one of the key components of the Three Lions side that reached the final of Euro 2020 and played an important role in helping guide the national side to the 2022 World Cup finals in Qatar.
His impact was hindered first by a serious shoulder injury as he underwent surgery in September and then subsequently by the form of Rodrigo across the Treble-winning campaign.
In total, 28-year-old Phillips has made 31 appearances for City and scored one goal, a penalty in the 3-2 Champions League group stage victory over Red Star Belgrade at Crvena Zvezda Stadium.
He won Premier League, FA Cup and Champions League winners medals in his first season and followed that up this term by being of the City squad that lifted the UEFA Super Cup and FIFA Club World Cup.
Phillips will now link up with the Hammers for the remainder of the 2023/24 campaign.
Everyone at Manchester City wishes Kalvin the very best of luck during his time at the London Stadium.