AFAIK the fairphone is the only phone on the market that is explicitly designed to be user repairable. It doesn't have a headphone Jack, though.

Unless you find a phone with an upgradable modem there is no „buy it for life” one. We’re now at 4th/5th gen networks and many places switched off everything older to reclaim wireless spectrum. LTE and 5G will be replaced too eventually.

IMO a modern phones usefulness is based in software not hardware. I'd find a phone that easily unlock and can run a ROM you like. I like Apple stuff but I think you're going to have to switch platforms to make this work.

An older Fairphone might work for you

A normal phone lasts about 7 years (pixel and iPhone update life)

Generally after that its not supported, even tho you could use the phone in an insecure state, but at that point I don't see why. Phones are simply not that fragile, and if you let it fall in salt water you have to change the whole phone probably.

Same problem with fairphone: They have replaceable parts, but even day 1 you can't say it would be secure in any way, and about 3 years in they just stop supporting it software side.

Even framework is only this good because they only have to manage the firmware and not the Linux install, former of which is only relevant to high security and not the average user

Maybe the Commodore Callback? It’s a modern flip phone, I think running heavily modified Linux, that leaves out pretty much all social media apps.