[Customizing checkout fields using actions and filters] Add new shipping fields to WooCommerce

wc-override-checkout-fields.php

// 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->get_id(), '_shipping_phone', true ) . '</p>';
}

For anyone wondering, you need to actually save the meta value or else you won't see it on the order page. See this answer: https://wordpress.stackexchange.com/a/376228/76433

add_action( 'woocommerce_checkout_update_order_meta', 'custom_checkout_fields_update_order_meta' );

function custom_checkout_fields_update_order_meta( $order_id ) {
    update_post_meta( $order_id, 'billing_colonia', sanitize_text_field( $_POST['billing_colonia'] ) );
    update_post_meta( $order_id, 'shipping_colonia', sanitize_text_field( $_POST['shipping_colonia'] ) );
}