Why does he stop calling?

Calling your special someone shouldn't be seen as an obligation, nor should there be rules regarding "the number of days to pass before calling him back" or "the number of days to pass before answering her phone calls".

talking over the phone is a means of communication, when you want to talk to your boy/girlfriend, then by all means dial the number!

having no initiative from either sides to pick up the phone and call the other is the MAIN reason why communication between "lovers" are turning sour.

how do you start over to avoid this? give him/her a call.