Easy, don't focus on the cell phone, focus on the driver's focus. Mandate driver attention monitoring, and require that prolonged inattention (i.e. N seconds c

Easy, don't focus on the cell phone, focus on the driver's focus. Mandate driver attention monitoring, and require that prolonged inattention (i.e. N seconds continuous, or N seconds of the past 3 minutes) results in escalating consequences, e.g. a warning chime, followed by activation of the hazard lights, followed by cutting the throttle and engaging lane keeping assist if available, and with several minutes continuous inattention, automatically call emergency services if possible. Ideally, phone manufacturers and car makers could work together so that the driver inattention chime automatically locks the phone and tells the driver to pay attention (or tells the passenger to tell the driver to pay attention).