If the phone was not enabled for web access, you will need to enable it via the configuration files, that you will need to provision and place in a TFTP server that your phone needs to point to.
There are plenty of threads you can review at CSC related to phone configuration with 3rd party PBX.
Assuming you want that device to register with a 3rd party PBX, you should have gotten one with 3PCC/MPP FW (which do have a full fledged configuration GUI), that one you got has enterprise FW, and even if you get to the GUI, it's a view-only GUI with basic device info and logs. All the configuration on your device needs to be formatted as if it was coming from a Cisco call control.
If you want to move to the 3PCC/MPP FW, see details at upgrade.cisco.com, fees may apply.
HTH
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