It looks to me that the default sorting is just presenting the actions in the same order they were found in the database.
We do have a feature request open on adding the ability to manually reorder them on the phone; folks that want to see this added should use the "Send Feedback" button in settings or send email to
omnifocus-iphone@omnigroup.com so the Support Ninjas can add their email to the appropriate item in our development database. Thanks!