You can check your gadget for originality by the serial number, Basic -> About this device, the data must match the data on the box and the device itself
You can also check the authenticity on the" Check Your Service and Support Coverage "page of the official Apple website, for this you need go to the page and fill in the appropriate fields, it will look like this
Check iPhone for originality is fashionable in several ways
For more details about each of them, see the article https://wifika.ru/apple-iphone-kak-novyiy-5-s-otzyivyi.html
In order to determine the original iPhone or not, you need to do a couple of things.
After all these points have coincided, you can safely understand that this is the original.
Well, in order not to repeat mistakes, you can read the story of this person.