Can someone sync my phone to their iPhone?

I'm curious, is it possible for someone to sync their iPhone with another person's phone? I've heard of various ways to connect devices, but I'm not sure if this specific scenario is feasible. I'm asking because I'm concerned about the security and privacy implications of such an action. Could you elaborate on whether or not this is possible, and if so, what steps would need to be taken to ensure that both parties' data remains secure and protected?