Swapping numbers from one phone line to another

Swap the SIM cards. When someone calls your phone number, they are calling the SIM assigned to it no matter what phone it is in.

FYI, the iPhone 15 Plus has an eSIM not a physical card 

Hey there @MMC2023,

We understand and would like to point you in the right direction.

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An eSIM, gotcha. Sorry for any confusion.

Apple has the instructions to move an ESIM from one phone to another

https://support.apple.com/en-us/HT212780#:~:text=Transfer%20a%20physical%20SIM%20or,tap%20Transfer%20From%20Another%20iPhone.