Modern iPhones are generally significantly more secure than modern Android phones, but so long as we're talking about (a) modern mobile devices (b) provided by Apple or Google, then I'm comfortable saying that all these devices are more secure than your computer --- which, for what it's worth, is littered with all sorts of little embedded doohickeys with code you can't see.

Okay good to know. Not sure who's downvoting you because this is useful info.

Now if we can forget the comparison between smartphones and computers, it would be great to know exactly which smartphones are a good choice for users of encrypted email. I'm on Android now only because it easy enough to root and use without any Google services (I prefer to self-host and use F-Droid for apps). I don't particularly like Android but it is the 'lesser of two evils' for now.

If I can do the same with an iPhone and never have an account with Apple I would definitely be interested as the iPhone hardware seems pretty good.

Basebands have not had full hardware access for quite some time now, due to their habit of being full of exploits that can be used to unlock the device. It's not just an iPhone thing.