Flexible filament is required for this object.
I designed this adapter to mount my old iphone 4s to the Skyblade 3D printed quadcopter. I used flexible Ninjaflex filament to dampen vibrations. The phone has a tight interference fit so it will never slip out on it's own. If you slide in the phone as shown, you can still slide the lockscreen camera grabber and use the volume button to start a video before takeoff. This design will probably fit many old phones, but I included the Fusion 360 file so anyone can customize.
v4 added some springiness that improves video quality significantly, and I put more zip tie slots so the angle is fully adjustable.