I'm questioning the evidence not the verdict. The fact that Nevill Bamber was unable to speak, for example, doesn't mean he didn't phone his son because he could have done that before he was injured. The fact that a wetsuit was found doesn't mean it was worn. The fact that people thought Nevill Bamber was careful with his guns doesn't mean that he complied with the law, he didn't. Even if Jeremy Bamber knew he could put 11 cartridges in the gun that doesn't mean he did.
You're right in tat it doesn't -(necessarily)- mean he didn't phone Jeremy. The question though, is WOULD he? Evidence exists to suggest he didn't think Jeremy could be trusted. It's very likely that there'd been some sort of contretemps between them that evening regarding a trailer Jeremy was to have bought back. It ended with Jeremy leaving and Nevill doing it himself. I feel it's highly UNlikely, that Nevill, knowing he couldn't be trusted to do his job, would have trusted him to even answer his phone, let alone get out of bed to do a rescue job.