Although there are a lot of bizarre things going on in this, MM's phone being taken and thrown is so weird to me....
IMO, there was significant rage in connection with her phone... Why would a murder-for-hire/stranger be focused on her locked phone? What could they possibly glean from that? And then, why would it be discarded right down the road? Why wouldn't they have kept it, if they felt the need to take it?
IMO, there is only one person who would have been interested in MM's phone for any reason, and that is AM.
JMO. moo