That kind of goes to the wrong end of the solution for me: Run-of-the-mill phones should be hardened, ultra-secure devices. We all have a right to privacy and security.
What we have now for work devices with manageable profiles seems to me to be a good balance that should possible to harden enough for extreme cases as well.
On the other hand "run of the mill" phones that you can hand to a teenager (or use as a backup phone) don't need ultra-security and the cost that comes with it.
Really low end devices would probably be secure by simple virtue of not having enough features to enable hacking.
Ideally, you'd want to build your own phone where you control the supply chain form hardware to software running on it. I do believe the US president has a custom NSA hardened phone.
Our phones are still pre-seatbelts, pre-crush zones, pre-lead-free gas, pre-standardized controls and signal lights, etc.
Our phones only meet electrical and rf safety standards. When one phone model one time had a bad battery, it was a big deal. But if someone steals your retirement, oh well.