New Every 2 - Only on Primary Line??

[bullynj]

Hello all, I need help. My husbands phone on our shared plan is due for a new every 2 its been like 3 yrs since he upgraded his phone, however he doesnt want a new phone and I need a new phone. My question is this, can't I upgrade his phone using his credit then deactivate the phone when we get home, activate it my line and reactivate his old phone? Verizon is giving me a hard time about using his credit saying its only good for the primary line, but I dont see why I couldnt do the deactivate on the new phone after getting home, its just like if we sold the phone and needed to reactivate our old phone.

Sorry if Im being confusing.