No, phosphoric acid is a weak acid.
No, it's a weak acid.
No, phosphoric acid is triprotic.
Nope. To my knowledge there are only two acidic amino acids: Aspartic acid and glutamic acid.
It is a weak, mineral (inorganic) acid. It may be worth noting that "weak acid" is a technical term; it's actually pretty corrosive and is not at all safe to play around with.