Would it be any kind of crime for you to carry a taser? I realize this is hardly an even substitute for a firearm, but whenever you can avoid death AND breaking the law I recommend it
The best way to survive any dangerous situation is to not be in it in the first place, or get out of it as soon as you realize you're in it. So I agree with your instinct to leave the situation and get to your phone and gun in your vehicle.
My first rule of combat is this: The best defense is a solid offense. But, since your workplace won't allow a personal sidearm, then skip to rule number two: If a responsive offense is not possible, establish a solid defense. In short, it may seem cowardly, but barricading yourself (and possibly others) or hiding has been keeping thousands of animal species alive on this planet since the beginning of the world. Engaging a superior enemy with inferior strength should only be done in one instance and one instance ONLY: when your morals or conscience absolutely require it, such as when defending your loved ones, or the ideals of your country in battle. Otherwise, engaging such an enemy is simply heroistic stupidity.