Here's how to filter to show contacts that don't have a particular detail saved:
- Go to the main Contact list by selecting "Contacts" in the navigation bar.
- In the page menu on the left, select "Add a filter" below the "Filters & Sorting" section.
- In the dialog that appears, choose a field based on what missing details you'd like to see, and then select "is empty." For example, select "Email" "is empty" to see contacts that don't have an email address saved.
- Apply the filter to see all of the contacts that don't have a value saved in the selected field.