functions.php

<?php 

function change_billing_fields( $fields ){
    $fields['billing_postcode']['label'] = '';
    $fields['billing_postcode']['placeholder'] = 'Postcode monkey*';
    $fields['billing_email']['label'] = '';
    $fields['billing_email']['placeholder'] = 'Email*';
    $fields['billing_phone']['label'] = '';
    $fields['billing_phone']['placeholder'] = 'Phone*';
    return $fields;
}
add_filter('woocommerce_billing_fields', 'change_billing_fields');

function change_shipping_fields( $fields ){
    $fields['shipping_postcode']['label'] = '';
    $fields['shipping_postcode']['placeholder'] = 'Postcode*';
    $fields['shipping_email']['label'] = '';
    $fields['shipping_email']['placeholder'] = 'Email*';
    $fields['shipping_phone']['label'] = '';
    $fields['shipping_phone']['placeholder'] = 'Phone*';
    return $fields;
}
add_filter('woocommerce_shipping_fields', 'change_shipping_fields');


function change_fname_field($fields)
{
    $fields['first_name']['label'] = '';
    $fields['first_name']['placeholder'] = 'First name*';
    $fields['last_name']['label'] = '';
    $fields['last_name']['placeholder'] = 'Last name*';
    $fields['address_1']['label'] = '';
    $fields['address_1']['placeholder'] = 'Street address*';
    $fields['address_2']['label'] = '';
    $fields['address_2']['placeholder'] = 'Street address 2*';
    $fields['city']['label'] = '';
    $fields['city']['placeholder'] = 'city*';
    $fields['state']['label'] = '';
    $fields['state']['placeholder'] = 'County*';
    return $fields;
}
add_filter('woocommerce_default_address_fields', 'change_fname_field');