You do have a valid point. I used to have a password with a backtick (`) in it. That is a standard key on a QWERTY keyboard but seemingly untypeable on an iPhone. I didn't realize that until I actually tried to enter that password on my iPhone.
Here's how to do it: Hold down the apostrophe key until a menu pops up showing similar characters, then choose the backtick.
Good to know. I am not sure if that is a relatively new feature, but a quick Google search didn't reveal the answer when I initially ran into the problem. It was easier to just change my password than to delve too deep into it.
Or change your password using a computer, to a more iphone friendly password.