$300 and up for a non-returned phone. (Could be even more depending on phone model) The return of the current contract phone covers the ETF since the contract is being terminated early in favor of an early Device Payment Plan device. The charge for not returning that phone on contract could realistically be higher than the ETF. So, basically, you add that charge to the total cost of the new phone. Depending on which phone you just signed an agreement for, that could be $1000-1200 total.
You will owe, but I don't think it is the $300 and up range. It will be $199 - here is from the FAQ
This is now called Early Device Upgrade Promotion:
If you’re required to send Verizon your current device as part of a recent early device upgrade promotion, you must send the device to Verizon Wireless within 14 days of receiving your new device, or you’ll be charged the early device upgrade non-return fee of $199.The device you send must be in good working condition, and the same one that was on the upgraded line. Learn how to send your device back to Verizon Wireless.
IDK, I don't see Verizon accepting $199 on a $700 phone that is 12-18 months old. But, that's me thinking S6 or iPhone 6. Perhaps the OP is sending back a lower-tier phone.
I think the math on the $700 phone is sort of like this-
you already paid $299 up front, plus $40 upgrade fee, and $20/month for 18 months = $699
One thing I trust Verizon with is not getting the math wrong . It is like Vegas, the house never loses. They are still making a profit on the early upgrades-- otherwise you don't get it offered.
Let us know to confirm it is $199 or something different. What ever you do, don't send a different phone back in hopes it works out. It won't. You will lose that phone and still get charged the same amount. Even if it is another 5S. It must match the ESN of the phone that was registered on your line.
My text messages I got from Verizon when returning a defective phone under warranty stated $299, but that might be different than a trade-in $199. Consistency, "we don't has it."