In short: Minimal.
Since the Automile Box has it's own built-in SIM card, and the data usage is included in the monthly subscription, you can compare the data usage of the Automile app to opening an email on your phone. The phone only shows information that is stored on Automile's secure servers.
This means that the app uses a minimal amount of data and doesn't use any of your phone's memory to store trip information!
If you have any additional concerns, please feel free to contact our support team via chat, firstname.lastname@example.org or (415) 749-9270