Brother in law has dementia which has been going on for 5 yrs now. Lately he has been talking on cellphone with no one on other end. Why?

I am wondering why he is doing this. I have been keeping a journal now for over a month before it was weeks apart and now its almost everyday and in that month he has talked on his cellphone to no one about 10 times. He is having vivid conversations of the past, his brothers who have already passed away, seeing people (he doesn't get out of his apartment to see any of these people who he is talking about), someone kicking in his door and him beating them with a stick, having a water gun in his apartment then he has a gun, seeing his nephews but they aren't around him anymore they are in the service. He sometimes talks for hours then sometimes only 5 minutes. He has learned on the house phone that you can turn on the speaker then you don't have to hold it well last night he was doing that same thing with his cellphone he was putting it down on a dresser then holding his cellphone above his head but as I said before no one was on the other end. He does this at 10am in the morning or 8pm at night there is no specific time he talks on his cellphone.

Is his dementia getting worse? His stories are getting worse, he will tell people that he is a prisoner in his own house, he almost got me kicked off the property by telling the manager things. He got turned into DHS someone thought he was losing weight and didn't see him but it came back unfounded.