1) The House smartphone → it is where you install everything truly vital, like the main bank app (started mainly because of this), 2FA apps like authy google microsoft equivalents, passwords, streaming apps (to do their 2FA), etc. This phone NEVER NEVER leaves the house, except ONCE if the bank app requires on location authentication of the phone for the bank app to function, which is common practice with traditional banks.
2) The Street Smartphone → you essentially create a ''street bank account'', deposit sufficient money for day-to-day transactions for some days or weeks, install the app, and only keep this app installed for any money use (many people also avoid even using the same bank as the main bank app, as the main bank usually is a traditional bank with physical locations to get help - and has tons of personal information stored - and the street bank usually is a fin-tech bank that people do not really trust like old banks, either economically or for security, but it has less personal data anyways). It also has the essencial social media like Whatsapp, instagram, some password manager like bitwarden or the apple-google cloud, and 2FA (the ones who actually use it) is avoided in this device.
3) the thief smartphone → many people like to take some old phone around to give to a thief if the need arises, this way even the street smartphone is saved. Might not work if the thief smartphone is too old or clearly broken though.
4) the work smartphone → the only mostly chill 2nd smartphone on the list, useful to keep private life separate from the professional life, and also is useful to avoid the boss sneaking into the worker's private life and devices. There was a scandal here when a provincial government out of the blue installed a whole app in the smartphones of teachers AND students with no warning or any control whatsoever, and many people got scared that the administrative google service app being used by all (google education or some s*t) pretty much allowed the devices to be remotely controlled and viewed by the employer , be it private or public, so many people assumed any work devices is or can be done the same.
Can you elaborate ?
What does this "on location" process look like ? What do they ask you to do ?
A disaster scenario in practice means you are screwed either way here, tons of physical documents can be lost or destroyed too, but that is a calamity that by definition is exceedingly rare.
Most are worried about common thiefs, a scenario of robbery or assault that can happen anytime anywhere and frequently, repeatedly. The overall threat here is far larger that the rare scenario.
Now, to the complexity. Usually the thief smartphone is some old phone still around, might not even be working, and no one puts anything in there, it is literally a throw-away device. It has no complexity or hassle, and usually is free. The house smartphone, people usually repurpose some old smartphone or buy a cheap android. I still have an iphone 6 for this purpose, and if the app is up to date, it usually is safe enough. People will not be using the phone for anything else, it will not leave the house, so exposition is severely reduced.