A cell phone question.

[LAS14]

Once again I turn to the smart people in this group even though my question isn't about "computers." Well... I guess these days a phone is a computer.

I have a Verizon flip phone and recently bought a no-contract Tracfone to use when hubby and I go on a trip. The new phone works fine, but I'm puzzled by the fact that in the Call list I see at the top "Primary Cell" and my original phone's cell number.

How does my new phone know about my original phone? And vice versa, I see now. Maybe I gave that info during the setup? Googling all forms of "Tracfone primary cell" is no help.

Is there a benefit to having the phones know about each other?

tia
las