Does your phone find the network at all? Or does it just not see it at all? Its possible your router is using N-only mode, and the Eris needs B/G to be enabled.
Look here: Belkin : Support : Changing the router's wireless channel and SSID
follow up to step 5, but rather than changing the channel #, look for where it says "Wireless Mode" and make sure it says something with "G" in it.
If that doesn't work, you might have a hidden network, in which case you can go into (on the Eris) Settings>Wireless Controls>WiFi settings> Add Wifi network. Then type in your network name, and password if there is one.