This could easily be changed at any time, as I may need to tweek it depending on how long this one lasts
I got a DJI Spark a week ago and have been using my nexus 5x with the controller. I have a Nexus 7 tablet I rarely use but it doesnt fit in the spark controller arms. So I modeled up a fake Nexus size block and two posts with a bracket on top that fits the Nexus 7 well....Note, I added 2% to the print in slicing to make up for some shrinkage and it was spot on.
I printed it today and just used it tonight. I had some screws laying around..3/4" #4 (sheet metal or wood screws are fine), with counter sunk heads. Used a counter sink bit to the printed holes to make them fit just right on the top and bottom pieces. 4 screws total. Printed in PETG.
View in OnShape: https://cad.onshape.com/documents/69057d51bc0b35a6b7eef7eb/w/5b144210a157a733396063a4/e/6800ac592d0402424c93f4b1
Printed in PETG (black), 10% infill for the tablet bracket for a little more flex and 30% for the posts and "phone" block that locks on to the controller. Im sure you could get away with changing those some. Supports are only needed for the tablet bracket.
May need to ream holes in posts to help screw together easier and use a countersink bit on printed countersunk holes for better fit.