There are plenty of ways to access the files on your iPhone, whether through iTunes, SSH, SFTP, iFile, or a multitude of apps. However, adding automatic network sharing to your setup takes quite a few steps out of connecting to your device.
I tried these in an attempt to get my video game media center to read files on my iPhone from inside the network. If you'd like to turn your iPhone into a shared network drive for any reason, there are two particular Cydia packages that you should try today...