Dilemma about returning/ getting new iPhone?

So about 7 months ago I bought a legit new iPhone with my Verizon acct because I was due for an upgrade. No insurance on it. Two months later it got shattered which was my fault. I went on craigslist and bought a used phone that checked out fine. No damage, not stolen, works fine, no problems. Another legit transaction. Recently it is having some slight issues with dropping calls, not a big deal. I called Verizon tech support to trouble shoot it and they were just like " hey you are still under warranty so we're gonna send you a new phone". They do not have knowledge of the original phone being broken and this second phone is what I'm using. So when I receive and activate this new phone, and I'm *guessing* I have to return this current phone (that wasn't the original) … Can someone tell me what scenario I might expect? Will everything just go on as as usual or will they be like " Hey this isn't your original phone!". If the latter, will I be able to " get back" my used phone that I returned? Is this too confusing to understand?

Life will go on as normal…

i won't entertain schizophrenic ideals, so ill ignore that "latter", as you call it.

Verizon doesn't do any part of the replacement. It is an Apple Device, so apple honors the warranty with this particular device.

This is an excellent question to ask the representative who orders your replacement phone. They will have your account up, the history of what phones are activated, a trail of where the warranty stems from, and be able to set an expectation as to what they are sending and what they are expecting back.