Found it! Yeah too expensive:
Kust Phone Holder for Cx5 Mazda,Wireless Charging Air Vent Adjustable Phone Holder,Mazda Car Vents Holds Mount for Cx-5 2017 2018,Car Phone Mount for iPhone 8 iPhone X,Smartphone for 5.5/6 inches https://www.amazon.com/dp/B07GNGXJ4B/?tag=m20b7-20
Thanks for digging for this. I had given up.
This item seems to provide a small custom plastic bracket that fits over the top and sides of the hazard light switch between the two center dash vents. It's not clear how it's mounted there, but it seems likely that an adhesive tape is used where it fits against the top of the hazard light switch and the sides of the center vents. I imagine the intent is that you leave this in place permanently. This small bracket, depending on the model you purchase, can accept two types of three-point phone holding brackets, one with a carbon fiber look and one that has a decorative finish similar to that on the vent trim rings, plus a magnetic holder which presumably works with a phone or phone case mounted metal plate. These options can be removed when needed.
I believe the three-point brackets use the weight of the phone to automatically tighten the two side clips against the sides of the phone. It doesn't seem to me that you would be able to turn your phone 90 degrees for a landscape view. You could do that with the magnet based model, though.
The mount seems to have an gimbal adjustment that would allow you to turn the phone toward you, the passenger, etc.
2018 MY CX-5 owners should note that the smaller bracket may not fit properly because of the air flow control dials present on the center vents of that model (U.S.)
My main concerns would be whether the small bracket could be removed without damaging the dash or vent surfaces, and whether I would like the appearance of the small bracket when I was not in need of the larger bracket such as short trips around town. I might choose the magnetic mount model, except that the metal plates needed on the phone or phone case can interfere with wireless chargers, in my experience, by producing unwanted heat.
The price is on the high side for phone mounts, but they did have to create a custom mount for the 2017 CX-5.
Unfortunately, no one on Amazon has reviewed this yet.