I'm not quite sure what you mean by where they are located. Is the question what desk they sit on or where they are in the PBX?
There aren't any comment fields where someone could enter free form text comments that someone could say "phone is on floor 2 SW corner" or anythnig like that. (Note to Mitel: Why aren't you doing that? )
If you're looking for the phone in the PBX, you can go to maintenance and enter "locate extension <exten>" and it will show you what PLID (physical location ID) it is. Not much good for IP phones but if your running digital or analog it indespensible.
A couple of other forms you can check out "Device Attributes" or in older software "change attributes assignment" form. This will show you any pick up groups, hung groups etc the phone may be in.
Another form would be "Multiline set group assignment". It will show you any extensions a number appears on.
Hope that helps and welcome to the Mitel world.
Ralph