Traccar client turns any smartphone into a GPS tracker (Android, iOS). It reports location to your own or hosted server with selected time intervals.
With the traccar-client device connected to the respective channel, you can get the telemetry data from your Traccar client app straight into flespi and store the data long-term.
You can follow step-by-step instructions on how-to connect Traccar client app to flespi here.
Note: by default, your traccar-client channel will start an HTTPS server, so use the "https://" prefix for the channel URI when configuring your Traccar application on the smartphone.