WhatsApp uses the phone numbers from your phone's address book. WhatsApp does not store any of your information on anyone else's systems. WhatsApp looks at the phone numbers in your address book, then checks to see which of those numbers are verified in WhatsApp. This allows any WhatsApp users from your address book to appear as contacts in your
Favorites /
Select contact screen and the
Chats screen. During this entire process, only the phone numbers are sent to WhatsApp for lookup, securely, over an encrypted connection. No other information, such as names, emails, and addresses are sent. So that you know who you are chatting with, the app then displays the names from your address book.