The phone cost me $325. Amex's coverage would only affect months 13-22 of my contract as after that I will be due for an upgrade. So if it gets damaged in months 1-12 I'm covered by Verizon; damaged, lost, or stolen in months 13-22 by Amex. And if it happens in 23 or 24 I get protection from Amex AND a new phone from Verizon.
Asurion costs $7.99 a month with a $150 deductible IIRC. Perhaps you're referring to their pricing for dumbphones?
In 13-22 AMEX will pay for $325 of coverage VZW (without Asurion) and AMEX will only cover warranty damage, not physical damage, lost, or stolen.
And how will that help when the phone by itself costs $700?
VZW/Asurion has a $5.18/month plan with a $99 deductible for smartphones. Look it up.