Devices listed under my Apple id

You probably had 3 other phones in the past that defaulted to sequential numbers as you signed in on them. Give them unique identifiers.

To change the name of your iPhone, iPad, or iPod touch, follow these steps:

On your device, go to:

1. Settings > General > About > Name

2. Tap the Clear Text button (X), enter a new name, then tap Done

From:

Change the name of your iPhone --> Change the name of your iPhone - Apple Support

Change the name of your iPad --> Change the name of your iPad - Apple Support

It is just the name assigned to your iPhone. You can change the name by going to Setting > General > About > Name.