He's getting the odd game or so and some late substitute appearances. But I think he'd improve more as a regular starter.
As a regular starter, your side counts on you. Your performances are critical to team success. This places an emotional demand on you which you'll need to learn how to cope with. Phoden would likely be the best or certainly one of the best players in whatever side he's loaned out to, placing further demands on his performance.
On loan he'd not only start more often - and be relied upon to produce with the attendant pressure and personal development that this entails - he'd also be exposed to a different management philosophy and would learn how to adapt to different coaches - and he'd experience a plethora of opposing talent in all-out, important, it-really-counts games where there's no holds barred, deepening his experience both from a purely physical performance perspective as well as from a mental and team perspective.
No... a loan for Foden would clearly have been much better for his development IMO.