Bear118 I think you're miss understanding their policy on that. I would call customer service and ask them if you're required to get a new sim when you get a new phone.
I believe Having the same SIM and moving it from phone to phone shouldn't really matter unless you're putting one networks SIM in a different network locked phone.
All of your service and identifying information (which is tied to your SIM), wouldn't change, unless you're using an eSIM then it might.