When my hand is holding my phone an moved in a certain way my pinky an ring finger starts shaking why is this?

Possibly ulnar nerve: The ulnar nerve is one of three major nerves that provide feeling and function to the hand. The ulnar nerve runs down the inside of the forearm to the heel of the hand. When you bend your elbow continually as using phone, ulnar nerve stretches around the boney ridge of the medial epicondyle.At elbow. The irritation of the nerve can cause symptoms, usually numbness, tingling, or pain.