Why do sodas use phosphoric acid instead of citric acid?

Hi, I'm an amateur dabbler/inventor and this is my first post here.

So I was wondering this. I haven't tasted the difference, could someone explain what would be the reason for using phosphoric vs citric acid?

Also was looking into powders and don't seem to be able to find phosphoric acid in powder form. Does it exist?

Secondly, if your product has too much citric acid taste, how would you balance it? I could add sugar, but what else would be useful?

Thanks for any input, I'm just learning.