You should take a look at GNU/Linux mobile operating systems every once in a while. They're making great strides and both popular GUIs KDE and GNOME have been working on making mobile a target in their ecosystems.

Fairphone comes with a five-year guarantee for repairs and parts, so none of that early planned obsolescence, and it works with all the Linux mobile distributions I have had my eyes on.

No planned obsolescence but they removed the headphone jack & started selling the earbuds which are one of the kings of e-waste compared to getting a nice pair of headphones or IEMs that will last a decade or more.

Try GNU/Linux phones, Librem 5 or Pinephone. They're repairable, with the headphone jack and lifetime updates.

Sorry boo, but the telephony is generally pretty garbage on all the Linux options & a phone still needs to be a phone. A lot of those important apps won’t be supported as well as they only cater to the Android/iOS duopoly.

Calls work fine for me on Librem 5. There are many posts on their forum with similar experiences, e.g., https://forums.puri.sm/t/librem-5-phone-review/21085

That’s one phone with overpriced features unfortunately. I understand you’re paying for a small batch, niche device (that some users have had a lot of issues getting the thing shipped) to get a slow CPU, measly RAM/storage, meh camera, & an IPS panel. I’d rather go the route of postmarketOS with BYOD that with better specs (even a 4–5 year old phone can easily outcompete) & an OLED panel, but much of the effort is not in telephony (I understand it’s all volunteer hackers, but it’s an unfortunate effect). The PinePhones have the same spec issues even with a better sticker price. It’s just too hard to justify. I flashed postmarketOS & Ubuntu Touch on an old OnePlus 1 which has similar specs & it’s gruelingly slow. Phones in the last 3 years are now all ‘good enough’ (hence sales across the board plummeting as upgrades have meant a lot less finally), so until the specs can get there, it’s gonna be a pass.

Even then you are yellow booting and that is another security issue.

What dumbphones you looking at? Everything retail I am seeing is a stripped down version of Android.

I don't know of any dumbphones on the market. I help people out who are on parole and they are not allowed to own smartphones. The best we can do is try to trick the parole agents by buying them flip phones, but even the most basic stupid flip-phones for Grandma still have Alexa built in and have some form of Internet access.

But remote attestation doesn't completely prevent you from running custom ROMs. Rather the problem is if you want to use various proprietary crapps/websites that insist on performing attestation. So there doesn't seem to be a point into choosing a "dumb phone" besides as some sort of protest. Rather for each of your devices you'll choose having a libre user-representing (ie secure) OS, or a locked down web TV equivalent. I'd personally choose my pocket device to be running secure libre software, and then use any proprietary crapps on a tablet that stays at home. If remote attestation gets so bad that I can't even do things like access store apps on a libre/secure device, then I'll carry two, with the libre/secure device supplying wifi AP to the other.

(this comment is most certainly not meant as any sort of defense of remote attestation)

The problem is, that's where the network effect bites you in the butt. With functioning remote attestation, platforms can lock down their APIs, so there often will not be a libre alternative. I.e. if your friends are on signal or whatsapp or twitter or whatever, you'll have to use a second phone to contact them, which will probably soon become your primary phone.

Sure, if things get really bad and I couldn't convince friends to use libre apps and/or texting no longer works, then I'd have to choose my main pocket device to be locked down. I'd probably still try to carry the libre device as a secondary one to have access to trustable apps while out, but I can see that being too inconvenient and giving up on it.

But my point was that still doesn't indicate moving to a "dumb" phone. A dumb phone is just a locked down device with even fewer capabilities.