At Manchester City, with the way City keep their wingers wide and push their “free 8’s” up high, Rodri is often joined in midfield by one or both full-backs, turning City’s shape in possession into something like 2-3-2-3 (or the old W-W).
This is fine, but can leave them susceptible to counter-attacks as it keeps their best recovery defender, Kyle Walker, in advance of the last line of defence. However someone like Phillips could slot in next to Rodri in midfield, meaning only one midfielder drives forward.
In turn with this, the back line shift would be asymmetrical, with the right-back and two centre-backs forming a three while the left-back (City are allegedly after Marc Cucurella) becomes the width City crave on the left.
This in turn lets the left-winger cut infield, making City’s shape in possession more like a 3-2-2-3 or, to it another way, a Cruyffist 3-3-1-3 (aka 3-4-3 diamond). This structure would essentially allow City to dominate the middle of the pitch while still stretching it wide and protecting themselves against transition and then, if need be, return to a 4-3-3 for defensive phases of the game.
Essential to this is midfielders who can handle themselves defensively, which is why Phillips is so perfect. His ball-playing and ability to break lines was honed under Marcelo Bielsa, who also loved the Englishman’s ferocious tackling ability in duels. He is a passer like all of City’s other midfield options but is also a much better defender as well (especially important if Bernardo Silva really does want out as the Portuguese is the only non-Rodri midfielder who comes close to being as solid a defender as Phillips).