Is the PVC broken flush with the concrete?
If the pipe continues to protrude a reasonable distance above the concrete, there may be a possibility for a coupling or the hub of a short length of PVC casing, to be added to further extend the casing above grade level.
If the break is down at the concrete level, then it's likely the concrete may need to be removed to permit an extension to be installed.
Adding an internal insert into the 6" casing would reduce the inner diameter of the casing. Although your casing is 6" diameter, and most pumps are only 4" diameter, you haven't stated which pump or other equipment is within the casing so we can't comment on the potential of reducing the casing diameter.