I don't use a cell phone holder (rather, an automotive GPS navigation unit), but I would recommend taking a look at Ram Mounts, as I've generally been happy with my Ram Mount that mounts to the seat mount holes. No drilling needed.
(not exact part I used but you'll get the idea)
RAM POD I WITH 1" SINGLE SOCKET ARM Unpackaged - RAM-B-316-1U | RAM Mounts
I bent mine so that it fulfilled the following criteria:
* did not lie directly in the path of any of the airbags (including but not limited to, side seat air bags, side curtain air bags, passenger front airbag)
* did not obstruct ability to view outside vehicle
* did not obstruct ability to view existing instrumentation
* easy to view and reach