Hi pattis, from the preamble; " superfluous letters in 12 clues spelling out a 2-word phrase, must be used to make good the shortages"
All of the letters in the 2-word phrase are required to make the 6 entries with shortages.
I'm wondering if Pattis has done the same as me - filling the grid and completing the shortages without waiting for the superfluous letters? I did that, finished it off satisfactorily - and only then looked for the phrase. The shortages were easily spotted.