I was not able to get a decent photo because of the shadows and such, but I did make a sketch of the problem
As you can see in the drawing, there is a gray vertical pipe which sends water upwards (like a fountain) from the deeper underground source when the rainbird is turned on.
The end pf the pipe sits about 1.5 to 2 inches under the level of the gbround, and cannot be removed or turned. It is jagged, like plastic that was broken off.
When we tried to attach a new replacement sprinkler, the result was having the sprinkler sitting several inches out of the ground, when all of the others are flush with the ground.
Since this is not a common problem (I can find nothing about it online) We were suggesting capping it with concrete. However, it would appear that we could take a piece of pvc pipe, slide it over the edge of the broken pipe. It could be cemented in place. The end would be capped with another end piece of pvc conduit end cap. This will stop the water from coming up out of the end.
But I want to make sure it will not ruin the overall system because the other sprinklers appear to work. I want to make sure that backing pressure into the pipe from the PVC cap will not cause a greater problem.
Otherwise, I say leave it alone. It may not look good, but it is at least watering some of the yard.