check number and country at checkout

wccheckout.php

add_action('woocommerce_checkout_process', 'check_phone_number_length');
function check_phone_number_length() {
    global $woocommerce;
    if ( !(preg_match('/^[0-9]{10}$/D', $_POST['billing_phone'] )) && $_POST['billing_country'] == 'RO') {
        wc_add_notice( "<strong>Telefon</strong> Număr incorect ! Trebuie să conțină 10 cifre"  ,'error' );
    }
}