The bedroom phone may have been in the bedroom. Jeremy had disabled all phones upon entrance.
Jeremy wiped off any of June's blood on the phone & put it in the kitchen, where Nevill was, off the hook.
Also a chance the phone was not there & June had not noticed.
Jeremy definitely disabled all the phones when he broke in by lifting the receiver if the kitchen phone, that’s true
But why and how did the bedroom phone get into the kitchen? The walkabout phone was away for repairs, and the kitchen phone which was a press button phone was hidden beneath a pile of magazines. That phone wasn’t broken — it was working perfectly — so why would June or Nevill have taken their bedroom phone downstairs? It doesn’t make sense.
I suspect it’s one of two things.
Either Jeremy asked them the night before if he could borrow the kitchen phone for a day or so on the pretext his phone at Goldhanger wasn’t working, or he made out to them that the kitchen phone wasn’t working properly and offered to bring their bedroom phone downstairs while they were all eating supper. He may have said he’d drop it off next day to get it repaired for them...
Then after he killed them all hours later, he simply put the regular kitchen phone under the pile of magazines. It was also noted that the wire had been wound round it, which is something you’d do if you’re going to take a phone away with you. You wouldn’t bother winding it round if you were just taking it from one room to another.
So I’m convinced he made sure that bedroom phone was in the kitchen before he left.
And as you say, when he broke in, he disabled it anyway...just in case one of them managed to get to the office phone.
