There is only one official WordPress app for iOS, and it works with both .org and .com sites.
To access your self-hosted (.org) site within the WordPress app, click on the link to “Add Self-Hosted Site”. Then, enter your username, password, and URL associated with that blog.
To get the most out of the WordPress app for iOS, they also recommend that you install the Jetpack plugin on your site.
Of course, you can always access a mobile-optimized (responsive) version of the WordPress dashboard from your iPhone by simply pulling up the admin URL within Safari, just like you would on a desktop computer.
Hope this helps!