In that case I would use the gryoscope like this (pseudo GDScript code, likely will not work)
"Place in _process, _physics_process, or some other function/method"
var gyro_axis = Input.get_gyroscope()
"Depending on how your phone is setup, you'll need to use"
"a different axis. I have no idea which axis you'll need. you'll have to test to find the right one"
player.rotation = gyro_axis.x
"You'll likely want to clamp the rotation"
player.rotation = clamp(player.rotation, deg2rad(-30), deg2rad(30))
As for the difference from gyroscopes and accelerometers, gyroscopes are for measuring orientation while an accelerometer is for "an instrument for measuring acceleration", according to Google. In your case you don't need the accelerometer since you're (presumably) not interested in the speed the phone is moving, but rather only it's tilt, which is what the gyroscope provides.