I still don't understand why throw the phone at all? If he is on the way to disposing of the body, why risk a stop and not just dispose of the phone with the body?
The smart thing would be to disable the phone and dispose of it with her body at the same time, otherwise it increases the chances of getting caught.
And If he is on the way back, and suddenly realises he still has the phone, why choose that location when he could easily destroy the phone completely ?
And having a phone wallet with all of Samantha's ID including driver's licence left in place is strange to me.
What also intrigues me, the accused was so meticulous in hiding her body, murder weapon, and other evidence relating to the crime. But then totally careless and nonchalant about the phone.
Things can change, too, as more evidence is collected since Samantha disappeared seven months ago