I still think the phone was tossed after Jen was left (assuming these events occurred on the same day). Since she was found farthest from the van, with the phone in between I think it happened on the way to drop off the van. I just don't see a nervous perp tossing evidence while transporting a victim.
I do think there is ambiguity as to when she was placed at the location where she was found and when the van was left in the parking lot as it was not noticed right away there by residents and the body was not noticed sooner and/or was not out in the elements for 2 months. The crime either happened in a very short time frame or was spread out with her body being moved and the van being left a day or so after she dissapeared. There are too many scenarios in my head to make a judgement. I hope LE has a better handle on the timeline than we do.