Have you tried a different phone?
Otherwise, I don't know... the way to put a Mitel 52xx/53xx phone into Teleworker mode is to hold down the 7 key while powering on and continuing to hold 7 until the "Configure Teleworker" prompt appears. If that isn't working, I would take it back to the office and connect it and make sure its working properly and try it from there. Also, once fully booted and registered, you can access the configuration menus by holding both volume buttons, then releasing one and while holding the other one press 2-3-4 in that order and release the volume button.