I use my phone while driving. Once a call is initiated or answered, I don't feel it's any less safe than having a conversation with a passenger. It's kind of a toss up in a sense because a passenger can look for hazards, but a person is also inclined to turn their head and make eye contact with a passenger once in a while, thus taking their eyes off the road, while if I'm on my phone, I'm always looking straight ahead. It's probably a lot safer than looking at your satnav, seeking a radio station, searching for something in the center console, etc.
I will also text while driving, but only while waiting at lights, not while in motion, and I still frequently glance up.
Obviously a younger, more inexperienced driver has not learned to multitask as well as a more seasoned driver, and doesn't possess the unconscious habits and perhaps 'muscle memory' for driving as much as someone older, though perhaps their reflexes are a little better.