Smartphones are common automotive fixtures serving music and providing navigational aid. Having a secure and easy to use mount is important. If you've looked around lately you'll see an overwhelming number of choices.
Consumer Reports tested 11 sub-mounts priced under $20 for ease and stability. They prefer the $20 iOttie HCLRIO102.
I've been happy with the slightly more expensive $25 Kenu Airframe vent mount. It slips on and off relatively easily, but has safely secured my device. It can double as a gadget stand with a card.