I very much doubt a jury would find guilty beyond reasonable doubt on the basis of whether or not a phone call was made. In the absence of satellite/digital technology proving or disproving the call it's entirely subjective.
If one doesn't believe the call was made then it means Jeremy must be guilty because he would have no way of knowing anything happened period unless he were there and falsely saying he got a call blaming Sheila is proof he was trying to frame her.
Whether one believes his claim he received such call is thus critical. The indicia of whether he received the call requires looking at his claims and his reactions. This is one of the things that had the biggest impact in me recognizing his guilt.
1) It seems implausible that Nevill would call Jeremy to disarm Sheila instead of doing it himself
2) It seems implausible that Nevill would get a chance to call Jeremy if Sheila were holding a gun on him.
3) The evidence establishes Nevill and June were attacked in the bedroom where there was no phone, this is where the episode began not in the kitchen.
4) Jeremy's false claim that he immediately called back upon the phone being disconnected
5) Jeremy's false claim that upon being unable to call back he immediately called police when in fact he called Julie.
6) When Jeremy did finally get around to calling police instead of calling 999 like someone w ho actually received the message he claimed would do he wasted time looking up phone numbers. After he found the phones unmanned at the first station he called he looked up another instead of calling 999 at that point even.
7) Not only did he have a lack of urgency before calling police he showed the same lack of urgency at the scene and even lied to police about Sheila's capability with weapons and how many there were scaring the police into inaction. Instead of begging police to do something he waited patiently for hours. He only went to the scene because police asked him to go there. Someone else would have either gone there before calling police or after without being prompted to do so.
This is without even taking into account that the moderator evidence establishes the call didn't happen and Julie ratting him out. The above is more than sufficient for a juror to believe the call didn't happen. If tha tis what one believes then Jeremy is toast.