Quad Lock and extra mounts are probably your best bet. That's what most of my friends use.

Everyone I know tried other mounts and switched to Quad Lock. Probably a good reason why.

I cheaped out and got a discontinued older model Delta mount for my old iPhone 4s. Worked fine, a great value for less than $5 because it was old stock. It's a bit bulky but the tough plastic frame protects the phone better.

But I used it for only a year. Too much clutter, between the phone mount, headlight and video camera. The video camera is more important (traffic safety).

So the phone is in my pocket now. If I need to take a call, return a text or check the map, I pull over and stop.

I did add a small bike computer to the handlebar, which is much smaller and lighter than the phone and does what I need. I mostly use it to check my real time speed and total distance. The phone apps record the activities.