As an ordinary consumer using my phone, how would I know when it's going to become unmaintained and I'll need to buy a new phone (if I want to continue having s

As an ordinary consumer using my phone, how would I know when it's going to become unmaintained and I'll need to buy a new phone (if I want to continue having security maintenance)? This is one thing I think Linux distros could do better: not just advertising upgrades to the next release, but warning when the current release is (soon to be) no longer maintained.