I made my stands for my Rift using cheap-assed Ikea floor lamps and a camera mount epoxied on top. 2 lamps make 1 89" stand (cut to length using a cheap pipe cutter), with the 2" camera mount, and 2.5" for the sensors, all coming to 93.5" in total...2.5" from my 8' tall ceiling. The lamps were originally $10 each, but they seem to have gone up. The best part of the stands is that the base is only 10", instead of 2-3 feet square that a tripod takes up. Fits nicely in corners, and also looks nicer than the legs of tripods. They're actually quite fashionable. :P

I looked into exactly the same thing. The "official" device made to help take downward-pointing photos of documents and such is called a "copy stand", but looking at those, I wondered if I'd be able to get the camera far enough away from the table when I needed more subject in the frame. The good ones seem pretty pricey, too.

I think a cheaper and more flexible solution (particularly since a phone doesn't weigh that much) is to rig up a microphone stand with a boom arm to do the job. Get a mic stand (one with a tripod base would be the most stable for this) with a boom arm attached, but rather than a mic clamp on the end, attach something like this:

https://www.amazon.com/CM01-Camera-Digital-Recorder-Adapter/dp/B001GWCC4I

Now you can attach any iPhone holder/mount that accepts a standard quarter-inch mount bolt, all the way from a cheap selfie-stick mount to something more rugged like the Shoulderpod S1, and everything in between. Between the boom arm and swivel on the adapter, you should be able to position your phone any way you like.

Good luck!