I didn't know there was a simple phobia of being robbed but I think this guy is right and you have it. In that case, the way to treat it is via exposure. Talking yourself out of it won't work. See treatment below:

http://www.changethatsrightnow.com/h...ment-and-cure/

My recommendation would be as follows:

1. Get a journal.
2. Get a friend or family member to help you with the treatment.
3. List the situations in which you worry you will be robbed from the least scary to most scary.
4. Have your confidant with you and expose yourself to those situations. DONT DO ANY VERY DANGEROUS SITUATIONS. Double check with the confidant to verify that they believe it is safe.
5. Record progress in journal. How scared where you? Did you in fact get robbed? How sure are you that you will get robbed the next time you do it?
6. Keep exposing yourself until you can do the situations on your own.
7. Continue exposing until the situations are no longer phobic.