It still requires a bank account, just a difference sense of the word. If someone only has a phone, they need to store their bitcoin somewhere, and its unlikely to be their phone. So whoever is holding their bitcoin is acting as their bank.
> If someone only has a phone, they need to store their bitcoin somewhere, and its unlikely to be their phone.
Why? Bitcoins do not exist somewhere, bitcoin transactions do, and they are stored in the blockchain. Bitcoins that you own are essentially unspent transactions to your address which is only a few bytes long.
A bitcoin wallet/address is not a bank account by any sense of the world.
I would sure hate to loose all my money because it rained hard while walking home. And all the other dangers that haunt phones.
A counter here of they should be backing up is unacceptable. Many people who are otherwise very knowledgeable don't make backups.
Sure, if they have all their money under a mattress then they are venerable to house fire, theft, and the like. But storing all their money on a cheaply made but affordable electronic device has the same problems, while opening up a ton more possibilities of chronic money loss.
What you need is to hold your private key. You could, for example, holds your private key somewhere else, and inject that private key to your phone when you need to use it.