About her phone, its possible SM just turned off her phone. Maybe she was tired and wanted to take a nap and didn't want her phone to disturb her. Maybe when she woke up, she left her phone off, and put it into her pocket still off when leaving for a bike ride. Its possible.
Not everyone is glued to their phones 100% of the time. When I sleep at night I turn my phone off. When I wake in the morning I leave my turned off phone on my night table while I get started feeding the animals and tending the garden(I live on a small farm). Sometimes hours go past before I go to retrieve my phone and turn it on.
The rest of what you say, about his truck movements, etc., I am not certain except to say that BM made a huge mistake in speaking to the police under those circumstances. Police can tell lies during questioning, and there are numerous cases of police railroading innocent people into confessing, etc. Despite the days of questioning, BM never confessed.
And I am not saying that BM could not have killed his wife--just that it seems unlikely to me, and that there isn't evidence to support it.