IMHO, we need well-enforced laws requiring manufacturers to do both of these things:
Provide service manuals and reasonably priced parts for a sensible period, much like existing requirements for replacement car parts. (Perhaps 5 or 7 years minimum?)
Put into escrow all the information needed for community support of these devices, to be publicly released when the official support period ends. (The easiest way to satisfy this might be in the form of source code, but data sheets and API documentation could suffice if they are reasonably complete.)
Some people have argued that the second point is impossible because phones are made with components that don’t come with specs or source code themselves. That might be true today, but if large economies start requiring it, then those component manufacturers will either fall into line or lose the market to competitors who do meet the requirements.
and not easy to load an alternative OS on.
This is another big one. We need to be able to unlock our bootloaders, install an OS of our choice, and re-lock our bootloaders. (Without permanently disabling any of the hardware features; there must be a way to fully revert to stock.) The only major brand smartphones I know of with a reputation for doing this right are from Google, which is kind of embarrassing.