I was traveling on a low cost carrier airline (budget airline) and found the trip frustrating as there is nothing to entertain me during my flight. I was able to utilize some items on the plane that can easily upgrade your seat with a screen for in flight videos. Total project is free of cost and took me less than 5 minutes to complete.
Take three barf bags from the plane pocket and detach the flexible thin metal piece behind it. You may have to borrow from your adjacent seats or ask from the flight attendant if you need more. Two of these metal pieces will serve as a base for your smart phone mount while the last piece will serve as a support on top of the smart phone to prevent it from flipping over.
Assess the possible mounting points on the table's locking mechanism in front of you. Depending on your plane seat design, bend the two metal pieces into Z shape and bend the last piece into a long J. The Z shaped metal piece should have an indention more than the thickness of your phone.
Find a secure slot/gap/crack on the table locking mechanism to install your phone mount. After attaching, make sure that the flexible pieces are stiff and does not fall of.The J shaped piece is meant to hold the top part of the phone. It may not be seen in the photo but I just wedged the end of the J-piece between the tight gap between the fabric and locking mechanism.