You can try Screen.Orientation
In the Start (or Awake) method of a MonoBehaviour that is added to the stage call:
Screen.Orientation = ScreenOrientation.LandscapeRight
Now you just need to check if the device is tablet or phone, I don't know any way out of the box to do this, but you can check the aspect ratio and base your decision on this.
You can check the aspect ratio by getting Screen.width and Screen.height.