There are some pretty decent portable controllers out there though (I.e. Turtle Beach Atom). Plus phone brackets for Series S/X controllers and DS4/DS5.
So there are good controller options, touchscreen controls for games designed for physical controls suck.
But carrying around physical controllers isn't very convenient.
I've plugged an Xbox controller into a phone before and that worked. I've not had an iPhone since they moved over to the USBC so I don't know about that.