My guess is, given state of the charging connector still attached but ripped off (https://news.ycombinator.com/item?id=38914210):

The entire thing fell out of plane (phone + charging cable plugged), then landed in a tree, where the charging cable got tangled in branches and that's when phone broke out of it and fell in grass.

So phone was able to release kinetic energy in 2 big events (+a few branches hit maybe), not a direct splash on the ground.

Wonder if somehow they can analyze the accelerometer data of the phone and figure out if that correlates with that scenario.