Remove my long gone phone from Finder, completely, forever

My Apple iPhone failed. I no longer have it. I fully erased it and returned it to the seller. I suspect it is on a trash heap somewhere or has been refurbished and sold to someone else. I still have a Mac Air and I use Finder. But Finder still shows this as available to me. I do not want to erase it because someone else might be using it. I just want it disconnected, forever, from me. I tried removing it in Finder, and it will not do that without waiting a month and even then, it will be recoverable. It asks for my phone number, but that phone number is now attached to a new phone, which is not an Apple. How do I make Apple Finder forget that phone, permanently, as if it was never my phone?