Written and stamped, signed, or whatever dive logs also help. Take your last or last couple or a printed version of your electronic log book with you, especially if you know you are going to a remote location. Just like you keep a copy of you passport. Be a boy (girl) scout - BE PREPARED!Some places you may dive can be so far off the grid they may not have the ability to surf the web for your information.
I think this whole arguement is silly.
Phones are fallible. They break, get lost, fail to charge etc etc etc.
Go ahead and travel three days to get to Triton Bay in West Papua, get there and have phone failure, and spend your vacation sitting on the beach drinking.
Cheers - M²