Ok. I have looked at the converted logs using dashware - with the caveat that I'm a rank amateur. Everything looks perfectly normal; magmod; battery cell voltages; motor loads etc throughout the flight giving no indication of any abnormality. I have extracted the relevant data for information and posted it below.
Examining the area of the data just before the sudden drop - and after looking at the KML file on Google Earth, it certainly looked like a fall from the sky to me - however I noticed that the throttle was continually being held down in various stages at the end of the flight with a corresponding reduction in height of the aircraft. And this made me examine a little more.
On the final few seconds, the throttle was reduced almost fully and the phantom fell out of the sky. Sorry to say it, but it looks like the OP got the throttle up and down commands the wrong way around.
You can see the traces below; The thin red line is the throttle. Anything below 0 is throttling down, above 0 is throttling up. The green line is the height of the phantom above the take off point - with the height represented on the RHS of the table so when the aircraft starts to "fall" it is about 5m or 15' above the take off point. The throttle is held down between 10 and 40% then released almost to the middle, then held all the way down as the aircraft hits the ground.
I'd almost bet that the OP is a pilot. They throttle up by pulling back on the sticks whereas with a phantom it's the opposite way around.
View attachment 46655
