Cell Phone Jammers means that anyone except white hats (or upper echelon black hats) can use cell phones around DC.
Castle Rock refers to WH and secureness thereof
I may be wrong here, but I always interpreted Castle Rock as possibly referring to Cheyenne Mountain - the Castle under the Rock. I found this link talks about the decode - I don't know if it's an appoved Q source but it seems relevant with the usual amount of salt. Or hot tea, as you see fit. (I am looking for the bourbon, personally)
https://threader.app/thread/1268761046682083333#:~:text=Cheyenne%20Mountain%2C%20the%20CASTLE%20under%20the%20ROCK%2C%20is,the%20Precipice%22%20at%20CASTLE_ROCK%20PATRIOTS%20ARE%20IN%20CONTROL