Removing 1- Prefix In Phone #'s

I read the thread below on how to utilize the Subsitute function to remove periods and thought about being able to use it for this. However, I have some phone #'s in my list that contain multiple 1- scenarios in them because the area code or 3-digit prefix sometimes include a 1- also. How do I make the formula only look at the 1- for long distance and not any other 1- found in the phone #? I want to remove all of the 1- for long distance because we are trying to use a new autodialer that is pre-programmed with the 1-.