Hey, guess what? It's the 21st century and people now have phones they can use to talk to people when they're out and about!
Honestly, you can whine and moan all you like, but they have a right to talk "for hours and hours about nothing" if they wish.
Now, if it's during the night or in a quiet coach, then that's the time when they should think about putting the phone down for a while, but if you're on the 12:00 or the 16:15 service then they can speak for as long as they like. If it bothers you that much, ignore it. You really shouldn't be listening to someone else's conversation anyway.
I was on the train today and a group of girls came and sat next to me and spoke to each other all the way. Did I complain? Not a chance, because I know if I was with someone I would be speaking to that person, and I know they have every right to speak if they want to. People speak, even if it's on phones or in person.
If I'm honest, it seems that many, many rail enthusiasts find nothing else to do but moan about the littlest of things. So people speak on phones when they're on a train. What business is it of yours?
And if you're actually considering getting a phone blocker just because people use their phones on the train, that's just plain pathetic.
Also, it's not just young women. If you actually bothered to take notes, it's young men as well. The whole "it's the young women who are the ones who speak constantly" idea needs to die a horrible death.