I'm not a fan of phosphoric acid . . .
Yes it will reduce alkalinity,
Yes it is the acid released from the malt in the phytin reaction, so it should be neutral
It reacts with calcium forming calcium phosphate (Probably as apatite) which deposits on heating elements and is fecking hard to shift . . . And what if your calcium levels are marginal??
And worst of all when brewing pale(ish) beers with high alkalinity liquors I am convinced that I can taste it
We can reduce the mineral content of the liquor using RO Water and use less acid, but that screws with other ion levels that you may want, meaning that you have to add something else. . . .whereas using an appropriate acid (sulphuric or hydrochloric) reduces the alkalinity and adds desirable anions.
YMMV, as it obviously does for a lot of US brewers