I've been next to a baby that was on full wailing for quite some time, despite the mother's best efforts and that was considerably worse than any idiot yapping on the phone. Didn't really want to make me throw myself or the baby off the plane, but I was quite happy I didn't have to deal with that every other hour of the day.
In flight the cabin air pressure is reduced as the plane goes up in altitude, to an equivalent altitude of about 9,000 feet when the airplane is at cruising altitude. This reduces stress on the airframe, by about 5-ish PSI on every inch of the cabin outer surface.
Adults have the ability to clear their eustachian by yawning, but babies generally don't. The extra air pressure causes their ears to ache for the entire flight.
That's why babies cry during an airplane flight. Mothers don't generally have to deal with it all the time.
(I wrote the firmware for one of the popular air cabin pressurization systems currently in use.)
Yes but a smart parent will feed their baby or give them a pacifier during ascent and descent. I was once on a flight where I literally watched the parents next to me feed their baby while we were sitting on the tarmac finishing the boarding process. That baby screamed for 3 hours after that. It finally STFU and then the dad started playing with it and took its favorite toy. It proceeded to scream for the next 2 hours after that. I wanted to cuff both of those parents on the ears for being complete idiots.