Maybe it depends on a lot of things like if your media server is running a standard OS or something proprietary.
If you are using windows you can use internet connection sharing to do it "maybe". It is done differently depending on the version of windows but microsoft has good instructions on their site.
The main issue you will have is if the tethering support for you phone has the option ICS needs to share it. For some reason not all the drivers you load for tethering have this support.
You also have to be somewhat careful about cpu load on your media server even very small spikes will cause delays and packet loss since the server is acting a router now.