I think mineral transportation cost would just be an error term in accounting for per phone build cost. This 100 gram phone costs $500.

Also cheap labour doesn't mean cheap in the overall sense. You would have to hire international workers at much higher rate, eg Emirates pays twice to pilots compared to US salaries. Also logistics of other parts will be more expensive. India is just on the verge of crossing the barrier where you could mostly do with local talent and local logistics. Africa is far from crossing that barrier.