yeefom, I believe there is a way to do this via a hidden setting; if you contact our
support ninjas, we can send you an email with a tappable link that will cause OmniFocus for iPhone to auto-sync much less frequently.
Why not post it here? Prior experience has taught me not to post hidden setting links all over the forums; folks find them and try to use them months or years later, sometimes without understanding what they actually do. Google, you are the best and worst thing ever. :-)