abs closet flange is 1 and half inch lower than floor. the flange inlet is ID 4 inches. I am thinking of use some abs cement to glue a new abs flange into the existing one. (I assume 4x3 flange can go fit snugly into a 4 inch inlet?) I did some google search but have not found anyone recommending doing this. Would it work?
Usually if the flange is not high enough, a larger wax ring is used or stack two wax rings together. Yours sounds like it is lower than any I have ever encountered. A good plumber with an internal pipe cutter could cut it with out damaging the floor, add a coupler, and with some proper material to hold the flange at the right height, reset a new flange. Seal that to the surrounding finished floor, so if the wax ring DOES leak, it will show on the floor, not go down around the pipe.