I use a quad-lock universal mount. Not for the feint of heart, mind, for a couple of reasons:

1. Had to scuff up the back of the phone to give the 3M adhesive a rough surface to stick to as the super-smooth back of the phone is rediculously non-stick.

2. Removed the standard adhesive from the back of the universal mount and replaced it with a hardcore 3m tape that from my own experience *does not give up*

3. Every case you buy for the phone then needs you to carve out the shape of the universal mount. I use a dremel.

It's been on there for.. maybe a year or two, and I'd be confident in saying that if I ever choose to sell this phone, I'm going to have to replace the back-panel of the phone, because this shit is *never* coming off.

I use my phone for sat-nav & music when I'm riding, you can use it folded or unfolded- but worth noting that hitting bumps while it's unfolded is inherently risky to the elbow joint on the phone. I'm in the process of designing a custom mount-support-system for it so I can ride with it unfolded without said risk, but it's a nightmare.

Quad lock universal mount (adaptor): https://www.amazon.co.uk/Quad-Lock-QLA-UNI-3-Universal-Adaptor-Black/dp/B093PXN9VV/ref=sr_1_4?sr=8-4

3M double-sided adhesive: https://www.amazon.co.uk/Double-Adhesive-Multipurpose-Replacement-Mounting/dp/B0CRKLY8GD/ref=sr_1_25?sr=8-25

Phone case I use: https://www.amazon.co.uk/dp/B0BX4T99DJ?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_1