Lulu Direct requires a valid phone number to be included with the shipping address when an order is created. 

There are free plugins that will allow you to make this a requirement at checkout. One good option is Checkout Field Manager (Checkout Manager) for WooCommerce. This will allow you to edit and modify all of your checkout fields.

Download, install, and then activate the plugin. Once the plugin is activated, you can make the billing and/or shipping address phone number field required on the WooCommerce Settings page under Checkout > Billing and Checkout > Shipping