What do you mean? As in a "Phantom Rule" was in the Exchange Mailbox or something client side?
I'm not sure if that is the correct term but a "Phantom Rule" is a server side rule that is actually there but the Outlook client does not reflect it. I think it's the result of an upgrade. The one site I saw it was an upgrade from 5.5 to 2003. I forget the utility from MSFT but they had the equivalent to ADSIEdit for an Exchange Mailbox to see all the real nitty gritty and edit it.
Or do you mean the silly user had their own private "Forward mail" rule created and forgot about it. Like "Forward all emails to this Group".
Of course reinstalling Outlook by proxy usually kills off the leprechauns, pixies, gnomes, fairies and other "Magical" creatures that would have been hiding in there.
Just don't tell anybody. It'll be our little secret.
Well all else fails, make an offering to the computer gods. Preferably in small unmarked bills.