pH is the fundamental thing, phosphate is the chemical patch that allows low pH water to be used. Basically they switched water source to something less alkalin

pH is the fundamental thing, phosphate is the chemical patch that allows low pH water to be used. Basically they switched water source to something less alkaline than what they'd used previously - and didn't do anything to mitigate this. The phosphate is kind of a "patch" to the problem of low pH. Fruit juice and cola is of course much, much more acidic than the Flint water - orange juice for example is about pH 4 (that is, 1000 times more H+ ions than pH 7)