I did not get my w-2 from my employer (Comcast) and I have no way to contact the office I worked for. There is no option for substitute form while filling out w-2

If this was your employer from last year, and your information was carried over from the 2016 return, you will need to delete the 2016 W2 in order to have the option of saying it is a substitute W2 when you enter the 2017 information. Be sure to make a copy of the 2016 W2 if you can, or at least copy the information you'll need, such as their EIN number and address.