No, talking in a car has no measurable impact on safety. And talking on the phone is obviously even safer than talking to other people physically in the car, since you don't need to take your eyes off the road or tour hands off the wheel like you would be tempted to when talking to another person in the car.

Plus, the vast majority of people have a significant need for social contact. Working an eight hour shift alone in a car without any contact with any social contact (except a quick sign off when dropping a package), 5 days a week, is inhuman.