spAIRtray says it's the world's first window shelf for extra room on most commercial aircraft window seats. Using it is easy. Just unfold it, insert one end of the back plate low in the alignment channel for the window’s sun visor and slide the other end into the channel on the other side of the window. Adjust to level out the tray and then you'll have some extra space for your phone, eyeglasses, snack, etc. The company says you can even hang a jacket on it.
"Installing" it takes just a few seconds. Now, the space on the tray is not a lot, 4" X 12", but in a cramped coach seat, it could be an enormous help. Dick did not try this with the plane in motion, but the non-slip pad certainly seemed like it would hold your phone or plastic cup in place. The holes on both ends of the tray are for your eyeglasses/sunglasses. While spAIRtray doesn't claim your tray is germ-free, at least you know where its been and you can clean it before you pack. It's washable in warm soapy water. And of course, it shouldn't be used during taxi, take-off, and landing.
The company did a careful review of TSA and FAA requirements, and says you should have no trouble using it in flight. It comes with a convenient cloth travel bag. $25.00 and it's Amazon Prime.