Fairphones have atrocious updates which means they aren't sustainable devices. They use a multiple generation old SoC from the beginning with an artificially shortened lifespan. Fairphones are currently designed and assembled by T2Mobile. T2Mobile even signs the firmware on the devices. Prior to the Fairphone 4, they had 2 previous ODM partnerships. They're limited to what their ODM offers which was likely the reason they dropped the 3.5mm audio jack when they moved to T2Mobile for the Fairphone 4. The working conditions and supply chain management are largely up to T2Mobile rather than Fairphone.

There's a severe lack of actual evidence for Fairphones having a more ethical or sustainable assembly and supply chain than Apple. It's likely each one takes more resources to produce and they definitely don't provide comparable updates.

You can buy used Pixels, e.g. from 8a up. I'd claim that this is much more ecological than buying a new Fairphone. I suppose that a Pixel is of a higher quality and has less defects than a Fairphone (which changed the ODM several times). --

This said, I would never use /e/ and Murena as I read too many things I don't like.