This actually happened to me about two years ago. The staff did a great job trying to retrieve my phone. I was sitting in first class and it slid under the seat of actor Michale Douglas. He didn’t care. When we landed in New York a mechanic came on, but could not move the seat. I went to lost and found at JFK, but they wouldn’t let me file a complaint because the phone wasn’t lost. People knew exactly where it was, under a seat on the plane. A week later I got a call from American Airlines, and during a maintenance stop they removed the seat got my phone and sent it back to me.
This was LAx to JFK