Why is the Demogorgon bugged when Will tries to contact his mother via phone? It is only suppose to sense blood from the real world. Further, why does it keep visiting Joyce through the wall even though there is no blood?
It may be chasing Will
The only times the Demogorgon comes out of the walls or ceiling in Joyce’s house are directly after Will has been communicating with her through the lights or phone. In the one instance, he’s been making the lights go on and off in a rather crude manner. In another, he was using the lights and the letters on the wall to communicate with her. As demonstrated when Hopper and Joyce enter the Upside-Down, creatures in the Upside-Down only influence lights in the real world when they are close by. Thus, Will must be literally in his house to communicate with Joyce.
Blood isn’t exactly the only thing that makes the Demogorgon emerge from the Upside-Down. Rather, it appears to be one way (the main way) that the creature tracks potential victims. Recall, for example, that Nancy sees it in the woods, even though she does not appear to be bleeding. The creature, for whatever reason, spends most of its time in the Upside-Down, and it seems likely that its ability to perceive the real world in the Upside-Down is limited. It’s also possible that it detects blood by briefly breaching the barrier and smelling the air, since we know it can make tears at will. But if it hears a human in the Upside-Down talking to someone on the other side? It knows there is fresh meat right there. So when it chases down Will, and Joyce is right there, it takes the opportunity to attack.