Common sense suggests that any activity that pulls your eyes away the road will impair your ability to see what's coming from the driver's seat. If you're looking up a phone number in your smart phone, you can't look at the car in front of you. If you're peering down into the fast food bag wedged between your legs, you're probably not simultaneously scoping out your rear-view mirror.
So it probably won't surprise you to learn that even people who are experienced drivers are more likely to crash while dialing a cell phone. Here, though, are some awfully specific risk ratios: An experienced driver doing this is about two-and-a-half times more likely to get in a crash or have a near-miss than if they weren't fumbling with a phone at all. And the crash risk for novice drivers goes up more than eight-fold. Just reaching for a phone makes a novice driver seven times more likely to have a crash or close call.