[Brian]

What content-type are the iPhone messages coming in as? Is it "text/plain", or is another MIME type being used?

Does the email address the phone is sending from on the "allowed from" list in OmniFocus for Mac's preferences?

Off the top of my head those are two things that come to mind. If that doesn't resolve it, please get in touch with the support ninjas so they can help. We try to get on the forums as much as possible, but we can't guarantee a response to every post; the support ninjas guarantee a response to every email.