If your phone has been stolen and you want to deactivate your WhatsApp account to prevent unauthorized access, there are several steps you can take.

First, it is important to report the theft to your mobile carrier and to the police. This will help to ensure that the phone is blocked and that the thief cannot use it to access your personal information.

To deactivate your WhatsApp account on a stolen phone, you can follow these steps:

1. Contact WhatsApp Support: WhatsApp has a support team that can help you to deactivate your account. You can reach them by email at support@whatsapp.com. Provide them with your phone number, including the country code, and explain that your phone has been stolen and you want to deactivate your account.
2. Use WhatsApp's In-App Feature: If you have access to another device that has WhatsApp installed and is logged in with your account, you can use the "WhatsApp Web" feature to remotely deactivate your account. Open WhatsApp on the other device, tap on the three dots in the top right corner, and select "WhatsApp Web". Use the camera on the other device to scan the QR code on the WhatsApp Web page that appears. Once you have connected to your account, go to "Settings" and select "WhatsApp Web/Desktop". Here, you will see a list of devices that are currently connected to your account. Click on "Log out of all devices" to deactivate your account.
3. Send an Email to WhatsApp Support: If you do not have access to another device with WhatsApp, you can send an email to support@whatsapp.com explaining that your phone has been stolen and that you want to deactivate your account. Provide them with your phone number, including the country code, and any other information that may be helpful.
4. Wait for WhatsApp to Deactivate Your Account: Once you have contacted WhatsApp support or used the WhatsApp Web feature to deactivate your account, WhatsApp will process your request and deactivate your account within a few hours.

It is important to note that deactivating your WhatsApp account on a stolen phone will not retrieve the device or data that may have been stolen. However, it will prevent anyone from accessing your WhatsApp account and using it for unauthorized purposes.