If you have lost your phone number which you used to register your account, it is important to take the necessary steps to protect your account. Firstly, you should submit a ticket to Gate.io's Zendesk support system, providing them with your account details and explaining the situation. This will allow Gate.io to investigate the issue and take the necessary steps to protect your account. Additionally, you should consider changing your password and any other security measures you have in place, such as two-factor authentication. Finally, it is important to keep a close eye on your account activity and report any suspicious activity to Gate.io as soon as possible. Taking these steps will help ensure that your account is safe and secure.