Why the hell ???... Spoilers

Why the hell did Paul smash the pregnant woman's phone when she tried to phone the police when they were all under attack in the house ?

Maybe i missed something but that made absolutely no sense to me why he would do such a thing !!!!!

Plus the final 25 mins of this movie was so out of tone from what had went before , suddenly it turned into a crazy slasher / Michael Myers type movie ! Really bizarre movie tbh !