Your fill-ups, services, expenses, trips and receipt photos are stored on the phone. They leave it only when you export them, share a report or make a backup. Android backup moves them to a new phone.
The location is used only while a trip runs, to measure its distance; there is no tracking otherwise. The network carries OpenStreetMap tiles to show a trip on the map, and Google's ads, their consent form and the ad-free purchase. Suggest an improvement sends the message you write, only when you send it.
The full text is the privacy policy.