I saw these at CES and the owner hooked me up with TWO stands for my chair. A standard size for my camera and one they built literally on the show floor for my phone, both attached to my chair in about 10 seconds.
The huge clamps are padded and fit on my Lasher frame tubing easily. After some on-the-fly adding of the component pieces, my phone was positioned right in front of me, accessible instantly and easily removable from the tension loaded phone grip.
The gooseneck sections are modular so you can add as many as you want to get the length you need. They have a great selection of other device holders as well, including tablets, cameras and of course, musical equipment like microphones and instruments.
The same gooseneck sections swivel around in any direction and are what makes these VERY accessible as you can position them in any way you like, bent, straight up, and even completely out of the way for transferring, with almost no effort.
I put mine on the front of my chair right below the brakes and wandered CES for the entire time, including getting on and off multiple buses and navigating the packed halls without it ever moving from where it was originally clamped.
These are so affordable as well, with the standard configurations starting in the forty dollar range.