A phone at four percent in a taxi with no charger is not a rare event. Neither is no signal on landing, roaming that has not activated, or handing the phone to a child for eleven minutes.
None of that is an argument against using a phone. It is an argument for one page of paper that works when the phone does not.
What goes on the page
Short enough to fit on one side, or it will not get printed.
6 things to do
Ticks are for this visit only. Nothing here is saved anywhere.
The address in the local language
This is the item that earns its place most often, and the one almost nobody thinks of. A taxi driver who does not read your alphabet can read the address as written locally.
It costs nothing to include and resolves the specific situation where you are tired, in the wrong place, and cannot explain where you need to be.
What not to put on it
Card numbers, passwords, and anything that would be genuinely damaging if the page were lost. This document is deliberately carried around, which means it should be safe to lose.
Passport numbers are a judgement call. They are useful for reporting a loss and are worth carrying separately from the passports themselves rather than in the same pocket.
Two copies, in different bags
One in hand luggage, one in a different bag or with a different traveller. The failure mode you are protecting against includes losing a bag, and a single copy in the lost bag helps nobody.
It is also useful when nothing has gone wrong
Handing somebody the page is faster than reading a reference aloud from a screen, and it means the person at the desk can read it themselves. Small, but it is the everyday case rather than the emergency one.