The assignment is due Tuesday Nov 8! I hate to inform you but Nov 8 is tomarrow, Thursday. In any event, you are just now starting that assignment ???
Do the program one small step at a time, and compile frequently so that you don't get overwhelmed with errors.
First step is to design the file format. From the looks of that structure each record needs to have the phone, address and name. Since address and/or name can contain spaces I'd suggest surrounding them in the file with quotes or separating them with a comma. The '\n' will be used to separate records.
Next you will need two functions -- one to read a line and save the contents in the structure, probably mygetline() can do that. The other function is to write out the data to the file.
When you get that done, post your results and we'll help with the rest, if you need it. But unfortunately for you I doubt you can complete this assignment by 9:00 am tomarrow morning, which is only 15 hours away in my time zone.