Convert number in call log to Gmail Contact
Both Dialer and Contacts apps can vary per phone model due to Android OS version, as well as manufacturer or carrier overlay.

Usually though, in the call log when you tap on the new number it gives you an "Add to contacts" option.  At that point it brings up a list of all contacts, so that you can add this number to an existing contact. However, there should also be a button to create a new contact, which is probably what you're overlooking.