I think you maybe misunderstood the work done by FairPhone.
First of all, they will be the first to tell you their phone is not 100% fair.
But what they want to proof is it that is possible to mine responsible in the DRC and Rwanda. The Dodd-Frank-act resulted in big companies simply avoiding resources from this region, which caused many problem for the people living from the mining industry over there. Sourcing from certified local mines is completely legal according to Dodd-Frank (which requires to prove it’s not a conflict material if it is sourced from this region), and supports people living in terrible conditions (instead of big companies with Canadian or Australian mines).
I would advise you to dig deeper into the website (like here: https://www.fairphone.com/en/our-goals/fair-materials/responsible-sourcing/+++) and the blog, which contains a lot of useful information (like these interesting articles). But also on the forum, the topic is discussed (like here: Details about the New Bugurama Mining Company (NBM)).
And of course, discussion is always interesting! So I hope others will join in this topic!