He's talking about electrical appliances that use 3 phase. Usually, industrial / commercial appliances that needs higher voltages/current. The plug looks different from your typical 3 prong plug. It has 4 to 5 prongs. 3 prongs is for each of the 3 phases.

TNB's 3 phase cable reaches your DB box only, from there onwards, electrical appliances inside your house runs only on a single phase.

About the energy loss via resistance, I am not too sure about that. However, I know 3 phase motors uses less energy than comparable single phase ones.

Yes. Changing TNB's single phase to 3-phase would not help you save electricity. If your house electricity supply has only a single phase, you should only consider going to 3-phase if the total electricity consumption of all your appliances(if everything is turned on at once) exceeds what single phase can safely supply you, which is about 60A I think.