If I've lost my iPhone and I'm trying to use Find My iPhone, how can I use two-factor identification that is being sent to the iphone I can't find?

I often misplace my iPhone (i.e. my daughter "borrows" it and I need to log into icloud. Today it asked me for the code it sent to my iPhone for two-factor ID. The iPhone which I am trying to find. Any clues?

Luckily this time I heard the ping of my Phone in her room saying I'd logged into my apple ID. But what happens if I legit cannot find it, or it gets stolen? Please don't say I have to call my carrier.