Does the accelerometer just return relative rotation angles

My app is trying to detect the movement and stopping of a mobile phone. GPS is NOT the solution.
Moving the phone around and printing out the acceleration, it appears it has nothing to do with the change in velocity but just relative angles. If the phone is at rest, you can get large numbers out of the input.

I think we are looking for linear acceleration outputs like m/sec*sec

The accelerometer does return the acceleration of the device. However here on earth we have a constant acceleration of 9.81 m/s² due to gravity. The accelerometer is usually calibrated that an acceleration of “1” equals 1 g == 9.81m/s².

Thanks to gravity we can even use the accelerometer to determine the orientation of the device relative to the earth, at least when it’s not accelerated in another direction.