Of course when you know the strength of the liquid acid, you can use Bru'n Water to calculate the additions of a variety of acids including phosphoric.
I had not seen that recommendation from Gordon before. Given that he and I live in the land of alkaline waters, using lactic acid is not the best choice because you would probably end up using enough to create a perceptible taste 'twang' from the lactate ion. I have never heard of its effect referred to as a 'harsher bitterness'. When used at most rates, lactic acid is pretty smooth tasting to me. Think of the last Berliner Weisse that had a harsh bitterness. I think Gordon confused his terms. In addition, all German beers are acidified with lactic acid (via acid malt) and I'm pretty sure they aren't harsh.
With all that said, if your water has more than about 150 ppm alkalinity to neutralize, you should move on to an acid like phosphoric. Phosphoric tends to be the most taste-neutral in beer.