You cannot retrieve the contacts because WhatsApp relies on contacts. For example, on a phone WhatsApp scans for users based on the attached contacts (phone/SIM/Google account/Samsung account) and since you don't have a contact application in Bluestacks, WhatsApp doesn't know where to look for. The easiest way is to install a contacts application from the PlayStore and then sync your phone contacts with Google. In Bluestacks, add the same account and sync the contacts back then go to WhatsApp and refresh the contact list.
