Text Replacements synchronisation between iOS and OS X does not work properly
First, to answer your questions:


Keyboard shortcuts do sync between OS X and iOS. However, in my experience this has always been quite slow, with the Mac taking a long time to recognize keyboard shortcuts I added on the phone.
Turning the synchronization off would require disabling the syncing of documents and preferences, which would also disable quite a lot of things that should be synced, so this is not really an option.
It seems that shortcuts are stored in several locations on an iPhone. Some of these can be deleted (which is what happens when you delete a shortcut), but some of them can't. These not-really-deleted shortcuts then sync again to iCloud, causing your problems. There is an Apple Forum post detailing how to delete the shortcuts, that you might wanna try (on your own risk, though.)


Now, for some fixes:


You could change your shortcuts. E.g. having a prefix like ;; in front of your shortcuts would make sure you only expand what you really want to. Also, it's not that much effort for typing. Similarly, I use l@g for expanding my email-address, which doesn't make any problems since I never type l@ anywhere else. This could be called a workaround, but as it seems it's the only option that should work reliably.
Using TextExpander you should be able to configure the sync more easily. However, I don't have any experience with it, and I'd recommend the first solution.