The default contacts app on Android has an export/import feature that will let you backup all the stored numbers into a .vcf file that you can then copy to a backup site.

This is not relevant to the problem at hand.

'Because it isn't "if" I lose my phone some day, it is "when". So, preparing for that is really important to me!'

The problem at hand is that he is afraid he is going to lose all his data.

The problem is when they lose their phone, how do they contact somebody without having their phone contact list. They do not have a phone to import this backup into. They do not have their phone on them to access a website with the backup. The backup ability is basically irrelevant, as all carriers can backup and restore your contacts seamlessly. It's the lack of the phone being the problem.

Presumably, we're talking about the short time-frame of a few hours between the act of losing the phone, and needing to contact somebody. The kind of situation where you ask somebody to borrow their phone.

I also keep a list of important phone numbers written on a piece of paper and stuck in my wallet. I started doing that when payphones were a thing, but I stopped doing that when I got my first cell phone. In recent months, I restarted the habit because there are times I want to just leave the phone at home.

I’ve done this by making every passcode a phone number for someone important. Mom’s phone number unlocks the computer, Dad’s phone number unlocks the tablet.