That's a build sheet.
If the details in the top right corner match your vin, then that's possibly better than what PHS can give you.
I have heard though that depending on where along the line that build sheet was used, it may be missing information that you're looking for.
I would guess, without knowing cars from that year as well as mine, that this was the option code for having all the provisions for a radio in place, even though it would have had no radio in place;
Cars without a radio had a plastic block off plate installed.
There is a reproduction available, but it's a 1978-1981 radio block off, so it's a bit bigger than the radio opening for a 1970-1977 Firebird.
EDIT:
BINGO!!
https://www.78ta.com/Pages/rpo.htm
(look near the bottom of the page)
UN9 Radio Accommodation Package