Nono, when you first enable it, the fields appear at the bottom of the screen.
There's a bunch of kinds of encryption to choose from.
If your first choice is 'none' and 2nd/3rd are some algorithm, then the default is to not be encrypted and an endpoint that DOESN'T support unencrypted communication would use choice 2 or 3.
Conversely, if you don't have 'none' entered as your last choice, then any phone that can't do encrypted calls will fail.