How do I mark a contact as private?

To mark a person or company as private tap on More icon and select "Make Private". This will classify your activity and communications (calls, emails, notes, files, texts, to-dos etc..) with this contact as private and not shareable with your team. 

On the contact's profile that you want to make private, tap on the More icon towards the upper-right corner. Tap on Make Private.

The lock icon indicates the contact is private.