Tutorial

// Hook in
add_filter( 'woocommerce_checkout_fields' , 'custom_override_checkout_fields' );

// Our hooked in function - $fields is passed via the filter!
function custom_override_checkout_fields( $fields ) {
     $fields['shipping']['shipping_phone'] = array(
        'label'     => __('Phone', 'woocommerce'),
    'placeholder'   => _x('Phone', 'placeholder', 'woocommerce'),
    'required'  => false,
    'class'     => array('form-row-wide'),
    'clear'     => true
     );

     return $fields;
}

/**
 * Display field value on the order edit page
 */
 
add_action( 'woocommerce_admin_order_data_after_shipping_address', 'my_custom_checkout_field_display_admin_order_meta', 10, 1 );

function my_custom_checkout_field_display_admin_order_meta($order){
    echo '<p><strong>'.__('Phone From Checkout Form').':</strong> ' . get_post_meta( $order->id, '_shipping_phone', true ) . '</p>';
}

//custom WooCommerce admin action

add_action( 'woocommerce_order_action_ezpocket_finish_pickup', 'process_order_pending_delivery_actions' );

//use $woocommerce->mailer() to send custom email with WooCommerce styling

function process_order_pending_delivery_actions($order)
{
    $order_id = $order->ID;

    $first_name = $order->billing_first_name;
    $last_name = $order->billing_last_name;
    $full_name = $first_name.' '.$last_name;

    $shipping_address = $order->get_formatted_shipping_address();
    $delivery_items = $order->get_items();

    $custom_data = get_post_custom($order_id);
    $delivery_date = $custom_data['_delivery_time'];

    $delivery_date = date_i18n('F d, Y H:i', $delivery_date);

    $items_list = array();

    foreach ($delivery_items as $key => $item) {

        $product_name = $item['name'];
        $product_quantity = $item['qty'];

        $item_row = '';

        $unit = ' unit of ';

        if ($item['qty']>1) {
            $unit = ' units of ';
        }

        $item_row = $product_quantity.$unit.$product_name;

        $items_list[] = $item_row;
    }

    global $woocommerce;

    $subject = 'Delivery schedule for your items';

    $admin_email = get_option( 'admin_email' );

    $to = array($admin_email,'[email protected]');

    $mailer = $woocommerce->mailer();

    $message_body = "<p>Dear $full_name,</p>";

    $message_body .= "<p>We will deliver your ordered items on this specific date. Below is the details :</p>";

    $message_body .= "<p>Order ID : $email_order_id </p>";

    $message_body .= "<p>Your items : </p>";

    foreach ($items_list as $key => $item) {

        $message_body .= "<p>$item</p>";

    }

    $message_body .= "<p><h3>Delivery Schedule : $delivery_date</h3></p>";

    $message_body .= "<p>Delivery address : </p>";

    $message_body .= "<p>$shipping_address</p>";

    $message = $mailer->wrap_message($subject, $message_body );

    $mailer->send( $to, $subject, $message);
}