All A2A websites work on all devices.
In April 2015 Google announced a mobile search algorothym change. It would rank sites that it calls 'mobile friendly' higher than other site that aren't.This is only for searches done on a mobile and not on a pc. And it would show as mobile friendly in the search results.
Google defines not friendly as 'having to pinch the screen'.
So whilst you may think that it's important for your page rank, it might not be.