I don't see anythng more "sustainable" in this phone compared to mainstream ones. Making it a bit more modular or repairable does not make it "sustainable".
They have a post about some of the reasons that the 5 was sustainable. It's not just the repair and modular parts but the whole supply chain. It' rarely gets talked about here as this is a mostly tech audience who focus on features, which are important, but Fairphone is more focused on the impact of the manufacture. https://www.fairphone.com/en/2023/08/30/is-the-fairphone-5-t...
"Fair materials" means nothing.
"100% e-waste neutral" is the same as claiming that you are "100% carbon neutral" because you buy carbon "offsets". It's dubious.
There are real positives, though: "100% recycled tin solder paste, 80% recycled steel, 75% post-consumer recycled plastics in the battery frame"