Phones certainly have distracted plenty of people going 70mph... some of those distractions have been fatal. I would imagine scant few of those distractions had been due to security breaches, but probably not zero.

We could imagine a following scenario: a clever virus spreads via zero day exploit to every iphone. The virus uses accelerometer to detect velocity over 70mph and initiates a bedlam protocol a minute after that. Your phone starts blaring maximally offensive content at max volume, controls are locked. Particularly effective when connected to car speakers.

The scenario is highly improbable, but there is a vector for a phone security flaw to be extremely impactful.