At the very end of the bowl filling up I am getting air bubbles in the bowl.What does that mean??

Sounds like there is some kind of blockage in the sewer line to me. Be careful how you flush or you could overflow the bowl and have a watery mess on the floor.

Can you tell for sure that the bubbles are coming back up from the sump area at the bottom of the toilet? Could be a partially blocked vent but don't worry for now if flushing is otherwise normal. Let is know if you start getting imperfect flushes or the bowl appears to be only partially refilled after flushing