You don't have to carry two phones. The idea is that the second phone stays home powered off and is used as an access token for the bank's website. There is no reason to carry it around. Pay cash in stores or use a credit card when cash is inconvenient.
I think this is a pretty outdated view of banking. I open a banking app at least a few times a day. In the EU just about every online transaction has to be approved in the app, we also use various payment apps for quick person to person transfers, use the app to generate disposable virtual cards for online purchases, etc.
I could cut myself off from the modern financial world and just use online banking like it's 2010 but that's a pretty big ask.
The US is way, way behind in banking P2P technology / fintech adoption. In many parts of Asia, even uneducated street vendors now accept digital payments via mobile phones (that's how easy it is). See - https://www.forbes.com/sites/pennylee/2024/04/17/the-us-lags... and
I would rather not have the kind of "financial innovation" that requires non-free apps running on non-free operating systems on locked down hardware. These apps, by design, track how people spend their money.