If they succeed in enjoining everyone else's smartphones, then yes, they are a monopolist, and should be held to the same standards that Microsoft was held to.
No, not yet (~30% share) but what you said it's not true. They cannot do "whatever they want." Eventually the Feds will start asking questions.
What kinds of questions will Federal Agents be asking Apple? What kinds of illegal activity are you insinuating Apple has perpetrated?
(edit: Disclaimer I previously assumed was unnecessary: Apple can't "do whatever they want", you are correct. For instance, if Tim Cook killed a hooker, that would be bad.)