Google has moved a lot of the platform code to their closed source parts. So for the purposes of security your typical Android phone is just as closed source as

Google has moved a lot of the platform code to their closed source parts. So for the purposes of security your typical Android phone is just as closed source as Windows. These days, unless you're running a classic Linux distro or BSD the OS code isn't auditable. And even if you were running Ubuntu on the phone the baseband is completely closed and almost always has memory access with no MMU so you should never trust a phone with anything important.