toilet fill

The water level in the bowl is determined by the design of the toilet and its enclosed drain trap. When you flush, the water level rises until the water reaches the output side of the trap and then any excess water flows out. See here:

Take off the tank top and flush the toilet. Is the water flowing from the refill tube running from the intake valve into the overflow pipe? The tube is what fills the bowl after a flush. It should be fast flowing into the overflow pipe when the tank is filling. If the tube is outside the overflow pipe, then that is the problem. Put the tube back in the overflow pipe. If the tube is inside the overflow pipe, but the water is slow flowing or not at all, or it shuts off prematurely (before the tank is filled and the float shuts off the flow), then replace the valve assembly.

This conditon may be indicative of a restricted venting system. Toilet discharges have to be balanced with with proper vent air flow and bowl fill to maintain the proper water level in the trap. Easy to check and correct. HTH

Joe