function custon_wcbcf_billing_fields( $fields ) {
    $fields['billing_number']['required'] = false;

    return $fields;
}

add_filter( 'wcbcf_billing_fields', 'custon_wcbcf_billing_fields' );

function custon_wcbcf_shipping_fields( $fields ) {
    $fields['shipping_number']['required'] = false;

    return $fields;
}

add_filter( 'wcbcf_shipping_fields', 'custon_wcbcf_shipping_fields' );