This can happen for a number of reasons:
1. You need to be using our VoIP phone lines to see call logs.
2. The call log will only show up if the contact and the phone line associated have been set up inside your CRM account.
3. You set up the contact with their phone number AFTER you made the call - it cannot create the call log as it will not know which contact to associate the phone log with.
You must set up the contact first with the phone number associated to it that way the call logs will register inside the history of the contact correctly.