WooCommerce email notifications contain a single block called “billing data” by default. If you want to add some additional fields e.g. a phone number you can either learn hooks and filters or if you use WP HTML Mail WooCommerce you can follow this easy steps:
Add custom billing fields to WooCommerce in 3 simple steps
1. Change the Template Edit Mode
If you haven’t already done switch your template edit mode to “Customize each email individually”
2. Open the your WooCommerce email for editing
Click on the edit icon next to one of your emails to open the MailBuilder
3. Replace the Billing Address and Shipping Address
Click the content area containing the billing address and delete the placeholder [BILLING_ADDRESS].
Then add each of the fields you want to show individually from the placeholders menu.