Getting object to mimick motion of iPhone

Say I have a mesh in the shape of an iPhone. When I left my actual iPhone I want it to lift. When I lower the iPhone, I want it to lower.

I'm currently trying out:

 void FixedUpdate( ) 
 {
     float y_acc = Input.acceleration.z + 1f;  // z is the iOS vertical axis, and 'at rest' has acc.z=-1 i.e. 1G gravity downwards
 
     rigidbody.AddForce( 0f, 100f * y_acc, 0f );
   
     if( transform.position.y <= y_min ) {
         rigidbody.MovePosition( new Vector3( transform.position.x, y_min, transform.position.z ) );

         if( rigidbody.velocity.y < 0f )
             rigidbody.velocity = Vector3.zero;
     }
 
     if( transform.position.y >= y_max ) {
         rigidbody.MovePosition( new Vector3( transform.position.x, y_max, transform.position.z ) );

         if( rigidbody.velocity.y > 0f )
             rigidbody.velocity = Vector3.zero;
     }
 }

This solution just doesn't work properly. While it does something, it isn't right.

I'm aware there is a random-walk problem with accelerometer data, that is why I'm having to sandwich the y values.

I am aware that capturing orientation is relatively easy. The gyroscope gives absolute direction reading.