Update: I created a mount for my Robo 3D R1 to mount this phone holder on the heated bed to capture better timelapses. Check out the video here: https://youtu.be/qNqM_ocIJ-0
This is a 3D printed phone holder that has a couple springs on the back that help it clamp securely onto just about any size of smart phone. There are also screw holes on the bottom to allow it to mount to different objects. I included a mic stand mount. It will slide and fit snugly into a normal microphone stand. And the phone holder itself will hold the phone without worry of it falling or sliding out.
This is a video showing my design process and talking a bit about the phone holder. Subscribe to my YouTube channel for more videos and creations in the future! https://youtu.be/jsq-GX1GQvo
I used PLA, printed at .3mm layer height using my Robo3D. No support material needed. I included two options here, after I completed the first one, I noticed there was more bend in the spine that I'd like so I created a sturdier one (the one labeled "sturdy"). So if you're decided which to print, go with that one. It's just got a thicker spine so it won't risk snapping as easily.
The only thing you'll need to do is add two springs to the back. They attach to little tabs I've added. I use some 11/32" x 1-7/16" Extension Springs (see picture) I found at a local hardware store. But some different sizes of springs could successfully be used and may fit your needs better. So experiment!