add_filter('woocommerce_checkout_fields','new_phone_field_classic_checkout');

function new_phone_field_classic_checkout($fields) {
    $fields['shipping']['shipping_phone'] = array(
        'type' => 'number',
        'label' => 'Shipping phone',
        'priority' => 111,
        'required' => false,
        'class' => array('form_row_wide'),
        'validate' => array('tel'),
        'autocomplete' => 'tel',
        'placeholder' => 'Shipping phone (if different than in billing)',
    );
    return $fields;
}