Thank you Laurence, I now understand that the Default Account option is not shown because I turned off the Contacts in both the Gmail and iCloud accounts. Only M&C account is turned on, so maybe there is no need to choose a default account.
The problem I have is when someone new calls me and I use their number to Create New Contact on my iPhone, the new Contact is not shown on my Desktop. It is shown faded on my Contacts in my iPhone. However, when I create a new contact on my iPhone by going to Contacts and pressing + to create a new Contact, then I can see the new Contact shown on my Desktop. What do I need to do to be able to use a number of someone who called me to Create New Contact on my iPhone and desktop?