I take back part of my complaint. 3 months after losing my phone on board when we landed at SEA, I got a phone call today that my cell phone had been found at the gate where we landed. I totally wasn't expecting that.
The phone fell out of my pocket at the seat, so I'm guessing a passenger / cleaner found the phone on board and turned it in at the gate. Not sure why it took so long to find out, especially when the customer service agent called over to the gate shortly after. But the phone was found which is good.