Most mobile shop clerks at Narita and Haneda do speak some English and offer online reservations in English so you could just show them a printout of your reservation. Android can be set to English language, even if it is a Japanese phone meant for the domestic market.

A tip on Google Maps - plot out your main attraction points and star them in Google Maps ahead of time, from your home computer. Then on the Android/iPhone, sign into the same Google account you used with Google Maps. You'll see the starred locations appear on the smartphone's Google Maps app, too. I find this a lot easier than trying to input it in Japanese or the English translation while on the go. Copy in Japanese, paste to https://www.google.com/maps (my language default is English) also works.