I know that Android phones let you change camera resolution. How can I accomplish the same on iOS?
Go to Settings > Camera.
You can select resolution and FPS for video & slo-mo. However, you cannot change the photo resolution.
You you will also be able to choose between high efficiency, using HEIF/HEVC, or most compatible, using JPEG/H.264. This does not directly affect the resolution, but does affect how large the photo and video files are.
Your phone's camera is limited by its hardware. Without opening the case and switching out several integrated circuits (and probably modifying the phone's firmware and operating system) you're not going to change that.
And you forget another thing that many cellphone camera enthousiasts overlook when talking about their hardware, and that's the optics. The main limiting factor of most if not all current cellphone cameras isn't the sensor at all, it's the lens that is actually responsible for generating the image.
That tiny piece of plastic (or glass if you're lucky) isn't really capable of providing the data needed for the sensors fitted to most modern cameras with enough resolution.
There's a reason why professional cameras have lenses with front elements that have a diameter of sometimes over 10 centimeter, and can weigh several kilos, and have sensors 24x36mm in size if not much larger in the really high end cameras.
You simply are never going to match that with your phone sensor the size of a nail clipping and ditto lens.
Camera+ 2, available in the app store for US$4, is a very powerful app I use instead of Apple's Camera app. It provides Manual Controls, RAW Capture and Editing, Depth Capture & Editing, versatile Shooting Modes, superb Photo Library integration, etc. If you are a seasoned SLR camera user or not, this app will help you get the most out of your iPhone's camera, even if you're shooting at the maximum resolution the iPhone can provide. I wish I was able to replace the default Apple Camera app with Camera + 2!
Disclaimer: I'm a contented user of Camera+ 2; and have no financial ties to LateNiteSoft S.L.