I had this happen a few times while going down the highway at 110, where there are crossings and a car up ahead crosses the highway, I wouldn't call it 'phantom braking' or even 'hard braking' though, it only slowed 5-10 km/h when left unchecked and then returned to speed as soon as the car cleared the highway. I think this is where the phantom braking gets overblown in that people use the term for any slow down which while they feel dramatic are not even using the brakes, it's just the sudden slow down using the regen braking.
I think as someone else mentioned, if you are driving AP/FSD with the foot ready on the accelerator and partciularly as you get used to how it reacts to certain situations, these can be virtually eliminated. I know in my case after the first couple of times, the subsequent ones only resulted in a drop of 2-3 km/h and were much more comfortable for the other occupants.