woocommerce/templates/order/order-details-customer.php

<?php
/**
 * Order Customer Details
 *
 * This template can be overridden by copying it to yourtheme/woocommerce/order/order-details-customer.php.
 *
 * HOWEVER, on occasion WooCommerce will need to update template files and you
 * (the theme developer) will need to copy the new files to your theme to
 * maintain compatibility. We try to do this as little as possible, but it does
 * happen. When this occurs the version of the template file will be bumped and
 * the readme will list any important changes.
 *
 * @see    https://docs.woocommerce.com/document/template-structure/
 * @author  WooThemes
 * @package WooCommerce/Templates
 * @version 3.2.0
 */

if (!defined('ABSPATH')) {
    exit;
}
?>
<section class="woocommerce-customer-details">

    <?php if (!wc_ship_to_billing_address_only() && $order->needs_shipping_address()) : ?>

    <section class="woocommerce-columns woocommerce-columns--2 woocommerce-columns--addresses col2-set addresses">

        <div class="woocommerce-column woocommerce-column--1 woocommerce-column--billing-address col-1">

    <?php endif; ?>

            <h2 class="woocommerce-column__title"><?php _e('Billing address', 'woocommerce'); ?></h2>

            <address>
                <?php echo ($address = $order->get_formatted_billing_address()) ? $address : __('N/A', 'woocommerce'); ?>
                <?php if ($order->get_billing_phone()) : ?>
                    <p class="woocommerce-customer-details--phone"><?php echo esc_html($order->get_billing_phone()); ?></p>
                <?php endif; ?>
                <?php if ($order->get_billing_email()) : ?>
                    <p class="woocommerce-customer-details--email"><?php echo esc_html($order->get_billing_email()); ?></p>
                <?php endif; ?>
            </address>

            <?php if (!wc_ship_to_billing_address_only() && $order->needs_shipping_address()) : ?>

        </div><!-- /.col-1 -->

        <div class="woocommerce-column woocommerce-column--2 woocommerce-column--shipping-address col-2">

            <h2 class="woocommerce-column__title"><?php _e('Shipping address', 'woocommerce'); ?></h2>

            <address>
                <?php echo ($address = $order->get_formatted_shipping_address()) ? $address : __('N/A', 'woocommerce'); ?>
            </address>

        </div><!-- /.col-2 -->

    </section><!-- /.col2-set -->

            <?php endif; ?>

</section>