When you call a phone number often, there's a physical memorization associated with the number. I think everyone has it, and it has less to do with knowing the numbers rather than knowing their placement on the telephone pad. I would venture to say that it has less to do with the location of the digits as it does with the movement of your thumb of finger on the dialing hand.

A few times, I've thrown myself off. I've tried calling a number I call often, but using my left hand instead of my regular right hand. And you know what? Messes me up most times. It screws me up so badly that my mind blanks out completely, and I need to restart with my right.

Give it a try. You probably have already.