That's a very good point about the phone. I have always thought he killed the kids before she got home and then killed her as soon as she arrived in order to prevent her from checking in on the kids and risking confrontation. But I have always wondered how the phone ended up there, since he apparently did not take the time to stage a scene. Maybe she was fast asleep by 2:30, and shortly after he killed her and then proceeded to kill the children. He would have had plenty of time to get them loaded in the car by 5:15, or around that time. But it does make sense that he would have hidden the phone before he murdered her, just in case. Jmo
I wondered if he hurriedly his the phone in the cushions while he disposed of the bodies, so that if anyone stopped by they wouldn't hear it ringing or something. Just a sort of panicked impulse rather than just turning it off.
But this makes more sense. He didn't want her to have access to help.