As far as e-waste goes from discarded smartphones goes, it is not clear to me that it is a problem we have to solve now, as opposed to just storing the discarded phones somewhere until it becomes economical to break them down for recycling.

Given the number of smartphones currently sold world wide per year, and allowing for reasonable growth, if everyone discarded their phone every year and those discards were all just dumped into a 1 km x 1 km pit, if you made that pit 30 m deep it would be able to hold well over a century's worth of phones.