Transfer line from Verizon, keep paying installment

Hi, so I'm looking to save some money on my phone plan. I currently have 3 lines, each with an installment plan. I want to transfer my number to a different carrier, and the other 2 phones/lines will stay on Verizon. I want to keep my phone (Pixel 2XL) and use it on the new carrier, but I want to keep paying Verizon the $18/month that the phone costs. The Verizon rep said that I can do this, but he kept reiterating it in an unconvincing way.

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Side-question: my Pixel 2XL is pretty beat up, lots of scuffs and dings along the edge of the phone. The screen is not cracked or chipped or damaged in anyway and works perfectly fine. But like I said, it's pretty beat up. Is it at all possible that Verizon would accept it to be traded back in exchange for wiping out my installment plan balance?