settings – What is the Phone Index in the Hidden Menu for Phone Info?

–OnePlus 7 Pro/GM1917/Oxygen OS/10.3.8.GM21AA/Stock ROM–
When I enter hidden menu ##4636##.
Select Phone info.
The first line under Phone Info says:
Select Phone Index, with a drop down menu off to the side.
Select drop down menu and it lists:
Phone 0/
Phone 1.
All of the info listed after Select Phone Index, is the exact same no matter which index I choose. Phone 0 or Phone 1.
What is a Phone Index?
Why are they identical?