The current software on the FP2 is based on Android 7, this doesn’t get any security updates from Google anymore, because it’s outdated. There is an update to Android 9 in progress, but nobody knows at the moment, when exactly it will be released:
A german thread about the update:🇩🇪 Update-Status Android 9 für Fairphone 2?
or here you can join the beta program: Fairphone 2 Beta Program
Because FP3 and FP3+ use the same core module and the same software, I would guess, that they will have the same livespan softwarewise.