Before you proceed, you need InTouchApp installed on your phone & InTouchApp Extension installed on Chrome or Firefox. Learn more.
How to Save an Unknown Contacts from WhatsApp to Phone:-
Step 1 - Open web.whatsapp.com in the browser and Scan the QR code by using WhatsApp on phone.
Step 2 - Select the contact you want to save.
Step 3 - On the top right side of the Chat screen on the Options bar, you will see a red contact icon - Click on the same.
Step 4 - It would ask you if you want to save the contact as Add New Contact or Add to existing.
Step 5 - Fill in the details and you are done.