Maybe we could try a couple tests?
Test One - The Current test
We should note the direction of current on the river and just throw off simulated phones (a close likeness in shape, weight, and material), and see how far it might travel before floating to the bottom and staying put.
While you are there, measure the height of the wall (you could just see where the wall hits you), the width of it (use your phone simulators to determine that), and make a note of it for test 2.
Test Two - The angle to the dangle
Prop a 2x?, measuring the same width as the measurement you noted while at the bridge, onto 2 supports measuring the same height that you also noted while there. A vacant parking lot might work for this, for example.
Put sand on the simulated water side to a little past the maximum distance you discovered would be required to get the phone to rest where it was found.
Again, using a similarly weighted object of a similar shape, see how hard or easy it would be to throw from a truck when it has stopped, when it is moving, from the drives side, and the passengers side and from coming and going in each direction.
You could do each several times and find which gave you the most consistent results.
Perhaps we will find the current had no baring, or perhaps we will find it had a LOT of baring on where our objects end up.
Maybe it would help us learn the velocity (or lack of it) needed to reach its final resting place.
Maybe we will learn it would have had to be tossed as far as one could possibly throw it (which couldn't be done from a moving vehicle cuz your throwing distance is restricted).
Maybe we would find that for the object to get there, the phone never entered the water from the bridge at all, but some distance FROM it.
Or maybe we would find that the object would simply sink pretty much where it entered.
We might be able to narrow down where it was required for someone to be to get it where it was.
We would find that the projectory of angle from a vehicle could not be achieved, thusly deducting that someone would have had to have gotten out of a vehicle, or been on bike or foot when they got rid of it.
Another thought here is, depending on what it would take to get it where it was, it might also help tell us who threw it.
Someone who had no resentment against michelle but was trying to help dale.
Someone who was desperate for help.
Someone who was really pissed off.
Or even just someone who couldnt really throw well from old age or a shoulder injury.
It is my guess you wouldnt really want it to be found in an area where people are likely to see it at some point as they walk across the bridge. Most people are likely to look over that away or pause for a look when crossing a bridge. Also, IIRC, that side of the bridge is indeed the side with the sidewalk, isn't it?
Could someone who knows post a photo of that corner and a description of the road/sidewalk/wall/road width, etc... layout there and the direction of current and so forth? Or even take on this entire expirement?