What iPhone model are you using?
It's an 8 plus
. The other photo was from a first-gen Pixel XL.
The photos I take with my phone look great on the phone unless I zoom in at all. I'm always surprised how quickly the effect becomes noticeable. Even the slightest amount of zooming in on the phone makes it apparent. You know how you can double-tap on a photo to zoom in
to a preset level? At that level it's unavoidable.
There are several things going on with a 2x zoom mode on iPhone Plus. There are dual cameras on the back, one camera has a normal
lens, the other camera has a ‘telephoto’ lens.Telephoto in this case meaning less wide angle
than the normal lens.
In good lighting the 2x double tap zoom mode in the camera app will actually use the telephoto lens for taking the picture, but will supplement the image processing with data from the other lens. So both camera modules are involved in making the picture.
If the room lighting is below a certain threshold, the iPhone Plus will continue using the normal lens, with a digital zoom mode, even at 2x camera zoom. The telephoto lens has a smaller aperture and the telephoto sensor is underexposed at these lighting levels.
You may find the artifacting you are observing changes when outdoors or in generally well lit environments.