At this stage your child has pretty good language skills for his age, and there are still a few things that he needs to understand, like the two crucial concepts listed below.
Concept of sharing
Despite your best and most patient attempts, sharing is a difficult concept for your child to grasp.
The connotation of the term "Mine" is something that children get well, but then that's subjected to their monopoly. For instance, when it's theirs, they totally understand the concept of 'mine'. But when it's yours, apparently it is also theirs. This applies to food on your plate, the phone in your hand, and the keys in your pocket, among many other things.
Concept of privacy
Your child understands the concept of privacy. When they are in the toilet they will say "I need some privacy mum, go away please", and you have to wait outside. Your child gets this one. But, when it is you asking for privacy, your child takes this as an invitation to stand as close as humanly possible, rubbing your legs, making creepy eye contact and asking you if you are ok. No actually, you are not OK, You want some privacy too!
So, the best way to make them aware of these stuff is by communicating with them. Once they have learnt to speak well, make optimum use of it by exchanging some productive words with them on such things.