Hi, feature with build in server is great. I use this the same way as You describe but and the end in command line, I add php script that is something like web server emulator.
/path/to/toy/php/bin/php -S localhost:8080 router.php
all requests are going through that script, if you are using nice url it's needed. I'm using such script for my projects instead apache or nginx. One thing that must be done in such script is support for content type header for images, css or javascript files.