What I've found works best for keeping access to photos restricted, is clicking on "Share" on the iOS photos app, and then selecting the target app (eg: FB Mess

What I've found works best for keeping access to photos restricted, is clicking on "Share" on the iOS photos app, and then selecting the target app (eg: FB Messenger). This means that the target app doesn't get access to my entire library -- but I can still share one (or a few) photos through it.