What if someone knows my iPhone passcode (not simple passcode) & restriction passcode? Lets say I was just taking a walk or was in a train or a bus. I had to unlock my iPhone with passcode there and use the restriction passcode. Somehow a person saw me entering the passcode and I realised that I was watched and that was after a long time.

Can that person do anything like remote access (SSH, VNC) or something about encryption keys? Lets say that person has access to a backdoor to my cellular carrier &amp; also knows my phone number (this means all my plain HTTP traffic, DNS queries, SMS, calls and other things can be seen, I am ignoring privacy policies here). What can that person do?
They can unlock your iPhone &amp; remove the restrictions... assuming they have your iPhone as well as the passwords/codes. 

Otherwise, nothing.