Your device is in SIP mode, so most options are none existent... Those options for screen saver and such are in the MiNet firmware only.
I get it, damn what a rip off. If I had known I wouldn't have bought it... Anyway thanks for the info.FX
Honestly, using a Mitel phone (like a 52xx or 53xx model) as a SIP device is gigantic waste of time and effort... Almost no features work, except basic feature access codes and speed dials, otherwise it's a fancy looking single line phone.
You are way better off getting a low end Yealink or Grandstream device, or even a higher end one refurbished, to use as a SIP device... I mean you can get a brand new Yealink T31P for under $50 USD shipped, a refurbished Grandstream GXP1620 for $30, or a refurbished Yealink T46G for under $65 (if you want to be fancy)... Tough to argue with prices like that... And all of them are far easier to configure and use as a SIP device. I love Mitel phones in MiNet mode, but in SIP mode they are kind garbage.