How to secure and iPhone against theft?

There is a popular post of Reddit right now where someone had an iPhone stolen AND the thief knew the pin code which allowed a complete take over of a digital life since they were able to reset the iCloud password with the pin code.

How can someone protect against this sort of attack? Specifically, if the person taking your phone forces you to divulge your pin code at gun point?

attack code digital icloud iphone life password phone pin point popular popular post privacy protect reddit reset sort stolen theft thief