To what court or arbitrator are you appealing? You do not tell us.
It may make no difference, however. The policy against phone calls while driving is reasonable. See the many studies which show that using cell phones impair drivers more than alcohol.
An "emergency" call? If it were an emergency, the caller would have called 911 instead of calling you. If you made the call, you could have pulled over to make the call.
Time to look for another job.