WooCommerce doesn't provide any phone field by default to the shipping and billing address forms.…
WooCommerce doesn’t provide any phone field by default to the shipping and billing address forms. This plugin adds the phone field to both the shipping and billing address forms and makes that field required (or mandatory).
Download and extract the plugin to the
/wp-content/plugins/ folder and activatee the plugin from the Plugins menu in WordPress.
This plugin will throw an error when the phone field in empty.