That looks pretty solid. I assume you will use some type of adhesive pad to bond it to the dash?
If you want something completely solid, you might be able to pull the center bezel back and locate a mounting point (bolt/screw hole or whatever) and possibly make a mount that attaches to that – then bends around the bezel (probably need to shave an 8th off the back of the bezel right where the mount is so it will close over the bracket cleanly.
Similar to the way Hab has hers set up in the pic below – but on the side you want and attached behind the bezel.

I would do this myself but I'm way too lazy. But looks like you know how to design things of this nature so shouldn't be anything for you and might provide you with a very solid mount with plenty of flexibility in terms of viewing angles. Would also leave a smaller footprint on your dash.
You could even run a power cord for your phone through the back similar to how I ran my GPS in the pics below. It makes for a clean install without cords running all over.
Or better yet, if you can do wireless charging with you phone, you could make the bracket and then mount a wireless magnetic charger and run the power cord through the bezel. Then you just slap your phone up there and not screw with any charging cables at all.
Just a thought though. Your design looks really solid as well with two attachment points!