How Do I Tell Which Model iPhone I Have?
These instructions only work on iPhones running iOS 12.2 and newer.
The model name and number should appear on that page.

Apple
How Do I Know If My iPhone is 7 or 7 plus?
To find the A-model number, you’re free to look in a few places.
Apple
On iPhone 8 and later devices, Apple stopped putting the model number on the phone’s back.

Apple
Again, you may need a magnifier to see the model number, as the text will be tiny.
How Do I Know If My iPhone Is 6 or 6S?
Comparing theways an iPhone 6 is different from an iPhone 6 Plusmight also help.

Apple
The 4GB version cost $599.
Both models required a two-year contract.
There is also an iPhone 6S and 6 Plus, which introduced pressure-sensitive 3D touch capabilities and gesture support.
The iPhone 12 series introduced 5G integration, improved photos and videos, Super Retina XDR, and more.