How would I reduce the number of clicks required to answer this LG phone handsfree in the car? The specs:
I have the phone LG Optimus G pro in a (DIY) car mount, there is no docking.
The NFC Tag system is not operational (case changes).
Magnet docking is not an option because of compass (navigation sensor).
There is no at&amp;t drive mode app running (does not help).  

The Operation in the Car:
An offline navigation app is running. Music is playing 50% of the time.
The music properly cuts down when a call arrives (great). 

The Event:
A phone call comes in, the phone popup covers the navigation screen, the call needs to be answered or rejected 1 click, or rejected with a SMS 2 clicks. The phone needs to be put into speakerphone mode 1 click. This method is not safe or simple for the drivers.

The Need:
The car is being driven, be that navigating a parking lot at 0 MPH or driving 70 the driver should be able to:
A) answer or reject the call easily
B) The speakerphone should already Be on

For the purpose of this question, Finding an app in the store does not help, unless you have tested it for months driving. I have done a lot of useless store research.

Method to use:
I need to know from experts who actually do this regularly How these methods stack up for the safest, most practical and least fallible for reducing the number of clicks?


Proximity, would proximity sensing be a reliable way of answering by putting a hand up to the general area of the proximity sensor without taking your eyes off the road? The possiblity to ignore (do nothing) and have the call eventually go to voicemail with zero interaction. Please explain why?
Voice, would talking to the phone in short phrases, knowing the bugs that can exist with speech methods , be a reliable and safe way to answer, would something with that complexity work every time?   Please explain why?
External power condition, Is it reliable to have a program use the condition of the external power plugged to set the speakerphone? (obviously this has a lot to do with the phone which is being stubborn).


It is a start:
The extended goal would be to also place calls while on the road, but one thing at a time.
No rooting
There will not be any rooting or ROM changes in the phone, these things are not an option at this time.
Time for the "standard-reply": tasker. I will not go so far as to give you a complete "profile" (as I don't use that exact combination), but at least a raw idea (as for general info on what Tasker is, please see its tag-wiki).


Tasker understands the required triggers, so you can use a combination of e.g.


power connected
proximity sensor
bluetooth connected
voice-control
call state (e.g. "incoming call" or even SMS)

Tasker can deal with the necessary actions, and for many more things there are additional plug-ins available. It supports e.g. (without plugins)


call divert (even restricted to certain numbers)
enable car mode
load or kill an app
volume control
popup task (e.g. with 3 buttons: accept, reject, message)
send SMS



Much more is possible. So you could setup your very special and personalized solution – not only for car-mode, but for many other situations. And while root would give you additional possibilities, it's not required for the described purpose (as far as I can tell).