I have a '23 C 400 GT, not a 650, but I have a few possibilities for you, or at least may give you some idea for crativity:
1) WunderlichUSA has a few mounts for the C 650 GT, for specific devices (which, unfortunately, doesn't seem to apply to your situation):
2) On my 400, I used a behind-the-windshield mount that I picked up on AliExpress:
I ditched the part that holds the bar, and drilled a hole in the other part, in order to mount a standard 1" RAM ball. If you're curious, I have seven pics and captions describing my work on this project, starting with this image in my 400 gallery:
3) Unfortunately, I just looked, and AliExpress doesn't seem to offer anything analogous to that for the 650. For the 650, I found these two products, is all:
4) Of course, I also found a lot of general-purpose phone holders there, with mounts that clamp around handlebars or short brackets with a hole to be held in place by a mirror stem.
But this sort of thing is nothing that you can't build with RAM products or RAM-compatible products found on RAM's site or hundreds of other places. If you're not familiar with those products, you might be interested in an
introductory article I wrote about such devices, eight years ago for webBikeWorld (when it was under its original management):
RAM mounts reviewed, a primer on RAM mounts
www.webbikeworld.com
5) You might want to be careful mounting modern -- and expensive -- phones. A few years ago, Apple issued its first warning about possible damage to a camera's stabilization hardware, when mounted on a moto.
There are a number of major players that have vibration-dampening mechanisms -- optional or built-in -- in or for their phone holders, such as Hondo Garage, SP Connect, Quad Lock, Peak Design, and RokForm. (I have an aging mount from Hondo Garage, and just bought a new mount from Peak Design over the winter).
6) An alternative to phone mounting is to get one of a slew of recently introduced CarPlay/Android Auto devices, which allow you to keep your phone in your pocket, or charging in a cubby, etc. These come with their own mounts, typically handlebar clamps, but of course you can alter that situation with mirror-stem mounts, etc., etc.
I recently bought a low-end, relatively inexpensive, unit like that from Aoocci, to introduce myself to the world of CarPlay. I mounted this on my Royal Enfield Meteor 350, and have a few pics and captions in my Meteor gallery, starting with this image:
More expensive such units are becoming increasingly popular, particularly those from Chigee and Carpuride. (I didn't want to go all out on this stuff, because I wanted to just dip my toe in. Also,
almost all of the time on my day trips I don't really care where I've been, where I am, or where I'm going.)
That's all I got. Good luck with your project.
