I want to my iPhone to forget my apple Id ?
Reset your phone to factory settings will remove it, but will also reset all the other settings (maybe not what you want ??).
Another solution could be to just "Sign out" of the Store "Settings->Store" - BUT if you have bought apps, and they need to be updated, then you still need to enter your Apple ID.
Can you perhaps tell us why you want to forget your Apple ID ??