The iPhone was one the few first phones to feature dual cameras. Only the plus model iPhone and the iPhone X (10) have this new feature. But why is it necessary? Why have two cameras? Well one is Optical the other is more standard.
Optical lens uses a visual zoom. This uses magnification, like a magnify glass, to zoom in. The iPhone supports up to 2x magnification anything further uses a digital zoom which removes the outer pixels and basically pre-crops the image. Optical zoom is better because when you zoom in the quality is not decreased like it is when you use digital zoom, although like digital zoom, optical zoom can only zoom in so much.
I you only have one camera on the rear of your phone chances are it’s not optical. That being the case your only zoom option is digital zoom. Digital zoom using the software basically to pre-crop and image. Think have you ever taken an image then crop it later only to find that it lowers the quality? That’s how digital zoom works. Although it has been improved with newer phones through camera improvement and software upgrades, it’s nothing compared to optical zoom. Digital zoom can also be found on many low level and cheeper point and shoot cameras. It’s smart just not to use the zoom if you have a digital zoom lens because you can always crop the image later.
Which is better to shoot with? Well an optical zoom lens is the obvious winner. The zoom magnification can make the difference between a good and clear picture and a blurry mess. Digital zoom cameras are easier and cheeper to manufacture. Also it takes up less space than optical zoom which needs more technology and space to to implement it, which is why is hard to place in mobile devices like the iPhone. If you try to zoom into something thats too far away and max out both optical and digital either way it will make a blurry pic especially with bad lighting.