Remove billing phone number field from WooCommerce checkout page.

custom_remove_woo_checkout_phone.php

add_filter( 'woocommerce_checkout_fields' , 'custom_remove_woo_checkout_phone' );
 
function custom_remove_woo_checkout_phone( $fields ) {

    // remove billing phone number
    unset($fields['billing']['billing_phone']);

    return $fields;
}