What is VPN on my phone

The answer to that rather depends on what you’re seeing.

There is a VPN client built into iOS. It is not configured by default.

A VPN is intended to be used to connect securely to a private network such as your employer or school to access resources on that private network.

There are many so-called public VPN vendors out there who prey on people’s ignorance and fear in order to convince them to a: give them money, and/or b: route all of their internet traffic through the VPN vendor.

VPN is a Virtual Private Network app that you put on your phone unless your employer added it. If you did it, there really is no valid use for it so it is recommended that you remove it.

It’s a system feature in settings actually.