Is there a way to generate an average cost or last purchase price for a Phantom Item? Is that the right question to ask?

I assume you are referring to an Assembly Item marked as phantom. If this is the case then the only thing I can think of is to post an inventory adjustment for Qty 1 at the cost you want. The average cost is only calculated when a transaction positively effecting inventory is posted. NetSuite then calculates the average cost of on hand qty at that time For LPP it is similar. NetSuite needs a transaction to base it off of Because the item is phantom a transaction will never be posted to it unless you make one up like an Inv Adj

Great info thanks