Car phone holders are available in many auto shops. However, I think my version works much better than the commercial ones and costs mere cents to make. It has the advantage of being extremely easy to make, takes up almost no space in the car and is easier to use, even without looking.
All it is, is a piece of Velcro glued to the dashboard and to the phone, so it hardly needs an Instructable to explain it, but it works so well that I thought this would be as good a way as any to let people know about it.
Step 1: What You Need
1. 1" to 2" piece of sticky back Velcro, both, the scratchy sided piece and the soft sided piece.
2. Some contact adhesive. (not essential, but may make a better job).
Step 2: Sitck It On!
1. Find a suitable spot on your car dashboard so that the phone won't be in the way when mounted there.
2. Glue the scratchy sided piece to the dashboard.
3. Glue the soft sided piece to the back of your phone (or the phone case if that's how you use it). Be careful not to obscure the camera lens, or get glue on it.
I find it is more secure if you use a small amount of contact adhesive for the gluing, but you can just rely on the sticky back that comes on the Velcro if you want - it just might come off after a bit of use.
You may notice in the picture that my phone is in a protective slim case that has perforation holes in the back. I took advantage of some of those holes to add a few cotton stitches around the Velcro as an extra way of keeping it attached. Not sure if they were needed.
The reason that I suggest the soft side goes on the phone is that it has a nicer feel when using the phone.
Step 3: Use It!
To 'mount' your phone on the dashboard, just reach out with your hand and push. You don't even have to look at what you are doing.
To take it off, use a twisting motion (see the picture). That helps prevent the Velcro from peeling off the dashboard. Its becomes the natural way to do it after a couple of uses.
There is an extra advantage that I have discovered since doing this. Sometimes, I have had my phone slip out of my pocket when I have been sitting in a particularly deep couch, chair or car seat. This can happen more when wearing trousers made of a 'slippery' material - not so much with jeans. I have found that the piece of Velcro on the phone provides just enough friction to prevent this happening.
Step 4: Be Safe!
Do not look at your phone while driving. Obey your local road rules regarding phones in cars.
With Siri and other similar apps it is easy to use the phone hands and eyes free - e.g. "Read that text", "Phone home", "Take me to 100 Main Street, Instructaville".