How do people get cubital tunnel syndrome or "cell phone elbow"?

Ulnar nerve pressure. Cubital tunnel syndrome is due to compression of the ulnar nerve at the elbow. Symptoms include numbness/tingling in the small and ulnar half of the ring finger, pain, and hand weakness. Extreme elbow flexion and pressure on the medial (inside) part of the elbow can exacerbate symptoms. With age and certain medical conditions, nerves become more susceptible to compression and tissues become stiff.
Ulnar nerve issues. One of the important nerves to the arm and hand, the ulnar nerve, which sits on the inside of the elbow can get irritated. This can happen in several ways, often because of too frequent and/or vigorous bending and straightening of the elbow or keeping the elbow bent for too long.