You can reactivate your WhatsApp account using the same phone number that you used before, as long as you still have access to that phone number. If you no longer have access to your previous phone number, you need to use your current one. A phone number is required to activate WhatsApp.
Uninstall and reinstall WhatsApp, next enter your phone number and confirm the OTP code that was sent to you in order to activate your account.
Once your account is activated, you may restore your backup (if available) to retrieve all your chats. Note that even if you no longer have access to your old phone number and used another one, restoring your backup is still possible.