The easiest way to locate the model name and number of your iPhone is by going to Settings > General > About. The Model Name is listed in the top section along with Name, Software Version ...
Under your device name or model, click on Phone Number to reveal the IMEI number ... On newer iPhones like the iPhone 6s, iPhone 7, and all subsequent models, Apple places the IMEI number on ...
If you have an older iPhone that can't upgrade to iOS 12.2, you'll have to do a little more sleuthing. You won't see an entry for the model name, but you will have a model number. However ...