check metadata in wordpress

When I made the registration form, I received the contact number from the users and saved it to user_phone Meta_key with the update_user_meta function to the wordpres database.
Now I have trouble verifying that no user enters a duplicate contact number in the field of the form.
How do I validate that if a duplicate contact number is entered during registration, it will show a duplicate contact number error.
Thank you for your help.