Unwanted Notifications on iPhone

I have an old iPhone, which I am using as a dedicated controller for my Sonos system. The phone has no sim card but is connected to wifi. I've turned off all notifications as far as I can tell, but every time my regular iPhone receives a call or a 2FA notification from Apple, my old iPhone gives me an audible notification. Considering that I spend most of the day at a desk with both iPhones, this is annoying because I keep receiving duplicate notifications. How can I stop receiving notifications on my old iPhone? Thanks.