You're supposed to cook lentils. Also, turns out lentils don't even contain that much phytic acid from the start.

Finally, your teeth rot? How? I suppose if you didn't cook the lentils, you might want to chew and ruminate them in your mouth for a few hours (tip: no, you don't), which might be long enough for the acid to have some effect on your teeth. But if you consume them like normal, and apply some basic dental hygiene, you're going to have to explain to me how this could really affect your teeth worse than most other foods (which are usually also slightly acidic).