I'm trying to avoid any hacking into my phone. I always keep airplane mode ON and once connected to a local wifi, initiate my VPN...which can be sporadic in China. My VPN has work-arounds but again those can be sporadic.
According to everything I know, it's still not possible to remotely hack an iPhone unless it has been jailbroken. The risk is that data will be intercepted. Your VPN should take care of that. Just don't start using the network unless and until you know the VPN is functioning.
anypats's suggestions are still excellent. Your other risk is that, when you cross an international border, you may be required to unlock your phone for inspection. The less data you have on the phone, the less chance you have of attracting undue attention.