Looks like textures on the Iphone X in that video is at least a quarter of the size, and stuff like grass pops in very close to the character unlike on the PC view
It does indeed. But are lower resolution textures enough to explain the fps/resolution/noise/heat differences between the two devices?
It's the same reason games run better on console than on a desktop with the same specs. It's not only the textures resolution but heavily optimised code for a specific architecture. Here in this case they're probably leveraging graphic instructions on this phone GPU that don't exist on the Intel integrated GPU