One way sync would stop your server syncing back to the phone, but wouldn't you still need the ignoreDelete option to stop deletions on your phone syncing to your server?
The trick is to sync to the import folder and let photoprism import them, which removes them from that folder anyways. So your phone deletes have no effect, since the photos are not in the import folder anymore. I have my imports run every 10 minutes, so there is never a huge buildup of photos to process at once. It's been working great so far