demo

Form Field Custom Validation

Set your data validation without limits, stopping next actions execution and returning a custom error message
Add at least these Actions After Submit
Copy this script into the Custom PHP Script action
				
					if ($ajax_handler->is_success) { // optional, only if no errors in previous verification/actions
    $user = get_user_by('billing_phone', $fields['billing_phone']); // change field Custom ID with your own
    if ($user && $user->ID != get_current_user_id()) {
        wp_send_json_error([
            'message' => 'This phone is already associated to another user!', // customize error text
            'data' => $ajax_handler->data,
        ]);
    }
}