I think the only option is to log into the admin area via the Safari browser on the iPhone. And then create a blog post entry on the Add Entry tab.
I'm pretty sure Safari on the iPhone won't be able to use the WYSIWYG editor. But once on the Add Entry tab, if you click the "Use Raw Html editor" checkbox at the top, then the WYSIWYG editor will change into a normal, plain textarea that
the Safari on iPhone browser should be able to type into.
I'm guessing the picture can be uploaded via the 'Upload Image' field on the Add Entry tab.
If you send me an iPhone, I can do some additional testing for you ... :-)