This is unfortunate and frustrating as many sites use it, a lot of people are frustrated that TinyMCE does not work on the iPhone Safari browser.
It's really frustrating although, I wonder if any other mobile phones are able to use TinyMCE or not, whatever the case is it would be nice to find a solution to use TinyMCE on the iPhone but it looks like it won't happen.
The problem appears to be that the iPhone does not recognize it as a Window that can be typed in, and you can't even paste text into it (was hoping you could type your content in notepad and paste it in, but that didn't work).
It seems like it shouldn't be such a complicated fix, interestingly enough all the controls for TinyMCE do work, such as the underline, italics, numbering, bolding etc.... and they actually appear in the content box.
This seems like a simple fix that the developer of TinyMCE may be able to workaround or something that really Apple should to, but how would we report a bug like this to Apple and would they even care?