I use the 9mm angled mount that @wspollack listed on my 400. Works GREAT with this holder:
I just can't use the X-Grip. I don't trust it. This one grips on all four sides pretty well. Never had any issues with it. I've used it the Galaxy S5 and S8. No worries with either one. ALTHOUGH... with any phone mount, make sure the mount doesn't activate any buttons on the side of the phone!
I may have had some issues with that once. ;-)

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I just can't use the X-Grip. I don't trust it. This one grips on all four sides pretty well. Never had any issues with it. I've used it the Galaxy S5 and S8. No worries with either one. ALTHOUGH... with any phone mount, make sure the mount doesn't activate any buttons on the side of the phone!
I may have had some issues with that once. ;-)