[throwaway_ab]

In the dark notice how much light comes from a phone and how much that illuminates the person holding the phone.

A car headlight shining your way from hundreds of meters even over 1km will often illuminate that person far more than their phone screen.

So if the phone screen is enough to undo the hour long eyes adjusting to the dark duration, then the car headlights at almost any realistic distance causes an undo.

[kragen]

a headlight a kilometer away may be spread over 36000 square meters including your face. (more detailed info on headlight antenna gain would be appreciated.) a 1200-lumen high beam over that area is 0.03 lux

a 500 nit phone screen emitting over about a steradian from an 80mm × 160mm area is 6.4 lumens, but at night you usually turn it down to minimum brightness, say 0.6 lumens. (i haven't measured.) at a distance of 300mm that steradian is 0.09m², so it's about 6 lux

so the cellphone is about 200 times brighter than the headlight at that distance, and that's also observable from looking at people using cellphones walking on the highway

but the person i was asking for more detail didn't specify that the headlight is pointed at your face; and in most situations where you can see headlights, they're not pointed at you. that's just a detail you filled in