Connect a computer to the router with an ethernet cable.
See the literature which came with your router for how to access the user setup screens in the router. Once in go to wireless security and review or renew the wireless security type and password. WPA PSK TKIP is the most common security type in use. Frankly, I would turn off wireless security while setting up.
Go to wireless mode and ensure that it's set to a protocol matching your phone's and your computer's wireless adapters (mixed mode is a safe bet). Check for a setting often called Access List that includes or excludes users by identifying the MAC ID unique to their wireless adapter. Disable that.
Disconnect ethernet cable.
Go to the phone's wireless networking setup screen and see if you can detect the router's SSID (wireless call sign). Select that network.
Apply the wireless security type and password to the phone's networking setup screen.