Code snippet to display the Shipping phone number in the FedEx Shipping label in place of the billing phone number. Required plugin: https://www.pluginhive.com/product/woocommerce-fedex-shipping-plugin-with-print-label/

gistfile1.txt

add_filter('wf_fedex_request','my_call_back', 10, 2 );
    function my_call_back($request,$order){	
		$phone = !empty($order->shipping_phone) ? $order->shipping_phone : $order->billing_phone;
		$request['RequestedShipment']['Recipient']['Contact']['PhoneNumber'] = $phone;
        return $request;
    }