I don’t think the dreadful bad mannered behaviour of speaking loudly for long periods on a phone, with the speaker also at full volume, is predominately younger people. When travelling on public transport I find it‘s more often those between the ages of around 25 and 40 who do this. The younger people tend to send more texts rather than speak on the phone. With older people it’s usually just a short conversation regarding where they are and what time they will be home. It can be rather loud if they are slightly deaf, but their short calls often amuse me rather than annoy me. There does seem to be an increase in middle aged men who are obviously gaming with their device on very loud volume during journeys on public transport.
It can be bad on trains but I find it even worse in the more confined space on a bus where you can’t escape them. I hope people don’t see my comments as being racist but I do find a large proportion of the people who speak loudly on phones with speakers on full volume are not speaking English. There‘s no excuse really for not using a phone in the traditional more discreet way. However, there are an increasing number of people who get on a bus with their phone speaker at full volume and have a loud conversation for the whole of their journey. The other week I witnessed a man doing this for a whole journey of over 30 minutes. I think it’s just extreme bad manners.
Sadly, I wouldn’t intervene, because you really do not know how some of these people would react, or what they carrying. I am very tempted to keep a supply of very cheap earphones in my rucksack and hand them out to people!