Can I make a pH 7 buffer from phosphoric acid and sodium hydroxide? I am an electronics guy with not so much knowledge of chemistry.
I would like to prepare a pH 7 buffer to test pH meters.

All web references I have found so far describing how to make a phosphate buffer use
disodium phosphate (Na2HPO4) and Monosodium phosphate (NaH2PO4) as ingredients.

I have a good supply of 85% phosphoric acid and solid sodium hydroxide. Can I make a pH 7 buffer from these ingredients instead or is there a catch?
You should be able to do this with little trouble.  The only caveats:


Make a stock solution of phosphoric acid and also of NaOH.  When you add them to each other to make your buffer, heating could be a problem, much moreso than if you were using the mono- and di-basic sodium phosphate salts.  So you may want to cool on ice when mixing these compounds.
You can calculate approximately how much NaOH and phosphoric acid to mix in order to get a pH 7 result, but it's best to use a pH meter to verify that you've reached pH 7.