IMHO... the iPhone in its first few generations fixed that what made previous "smart" phones horrible; not so much buttons, paramaters to set and therefore a much simpler UI.
Through the years many new functions, options, different looks have appeared in iOS, all with good intentions but I have to agree, for those who start with an iPhone from scratch... it is a time consuming thing if one has barely any clue what all these "things" appearing on the display mean. It is even more complicated when non-Apple applications/services are involved - multiple accounts, app stores, data plans etc etc.
Apple could make it simple again by starting the setup of an iPhone with a question if the user just wants a simple phone with big icons, big text, photos and maybe FaceTime. The anti-trust agencies probably might complain again, but with this use case it best to keep it simple and keep out 3rd party crap.
I really think just having a "senior" mode at startup that bypasses everything, so it can be used right away, will fix the issues. Also, making the function simple, so getting them to unlock with multiple presses is no good. Even when I tried to unlock it from an angle, it didn't work, and then I picked it up and discovered it needs two presses and their finger. However, none of them could gauge it. Face unlock was better in some ways and worse in others, as for some reason, they all wanted to put the phone right next to their face to unlock. Then they swiped, and it would do that thing where it would bring the screen down for one-handed use, lol. Then they'd click on things, not expecting them to open, and get lost, lol.
Things just need to have one deliberate use. For example, trying to use the home button to unlock on the SE was a nightmare; it needed a very specific press, otherwise, it would bring up other things. Then, suddenly, they were in the multitasking window or Siri asking if we want to enable it or a hundred other things, lol. For some reason, they wanted to do a long, hard press, not this light, quick one the fake home button needs, but finding my old iPhone 4S, it works fine.
They do not want passcodes either. We'll just have to accept they might lose their phone; security isn't important to them, and they want to go to a bank to do their banking. They want a camera to take pictures. I tried showing them all how to use the camera, and they hated it. You need a proper physical button and a lens that moves like an old camera, lol. So, these phones are literally just a device to phone people; none of them could even work out how to text. Honestly, if you could never set up the phone and just phone people and have the number pad showing all the time, they'd be happy with that.
Again, the Nokia "dumb phones" have this annoying way to unlock the keypad, and none of them could deal with it. I was hoping the iPhone would be easier; I looked like a right idiot, lol. Then, if you didn't have the keypad locked, honestly, everyone's phone had dialed "999" several times. Like, we need 911, not 999, and why are the phones only dialing 9?
Anyway, I'm trying flip phones. I think if I can boil it down to "flip it open to pick up, close it to hang up," then I'm fine. As long as the phones do not do anything like requiring you to press a button to answer and hang up, I'm good.