I bought the following cell phone holder for my iPhone 6S:
Cellet Adjustable Automobile Cup Holder Mount for iPhones, iPods, Smartphones, MP3 Players, GPS Systems - Retail Packaging
by Cellet
And placed it into the cup holder on the left side of steering wheel, under the left air vent.
It has worked perfectly for me.
You should check your local motor vehicle code for when you can mount cellphone, gps, etc...: in my state you can't mount anything onto the windshield - you can get a ticket for this violation.