Why is my phone display dim?

The phone display on the head unit is usually dim but lights up sometimes.
It changes on it's own randomly with no input from me.
I used to ignore it but it is bothering me now! LOL
When it's dim (greyed out) there is no touch response.
I'm not sure why. How can I fix it?
FYI using an Android phone
Thanks

 

I think it has to do with whether the car is in motion. Brightest at a stop but dims when you start to move above a certain speed

 

Thanks, I'll have to check that out.

 

Turn off nighttime mode on HU.

 

Have the truck stopped and add a contact to that list by pressing and holding and selecting one.

Start to drive and you will notice when you drive above ~5 mph that the contact that you added will still be selectable (i.e. not greyed out), but the other three 'Select and hold to add contact' buttons grey out.

This is a safety feature (just like initially pairing a BT device to the truck) that keeps you from trying to add a new contact to that screen while you should be focusing driving.

It doesn't have anything to do with nighttime mode or anything else.