It's a trend that's been going on for a long time - I don't mean only the loud two-way conversations on mobiles (which in fact is not restricted to the younger generation).
I call it individualism - I think we are beginning to see the end results of our individualistic society, where collective responsibility matters less and less, and any talk of the common good and social co-operation is seen as some kind of "wokery" nonsense. "No-one's-going-to-tell-me-what-I-can-or-can't-do" is a variant of the type of comment that popped up regularly during the beginning of the pandemic, when the government was feeling its way around the public-health problem.
Any curtailment of activity was seen as an infringement of individual right; either interference by the state or 'busybodies'.
Two incidents that, to me, highlight the selfishness (and arrogance) of our individualistic culture; a hen-party in a popular restaurant in Sunbury-on-Thames, late 80s, where the male-stripper was at the table, contorting and writhing so close to ours (late ex and me) that he was spilling our drinks. There was no room to move our table, but the hens could've moved theirs enough to make room for their stripper - which my ex asked them to do. "No" - "we booked this table, tough luck" kind of response.
Many years later in a rather nice pub in the Cotswolds having a quiet drink with my now OH - when smoking was still allowed - I asked the few patrons if they minded if I smoked, over in the corner of the pub away from the bar, and said if anyone objected I'd be happy to step outside in the garden area (this was winter so no-one outside).
There was a stunned silence which I took to mean a 'yes-we-do-mind', so slipped outside to smoke. Much later the barman told me that the 'silence' was because the customers were shocked that I had bothered to ask... they expected smokers to just smoke where and when they felt like it.
I think the individuals with their speaker-phone conversation mentioned in the OP are part and parcel of the same trend - some don't give a fig or thought to anyone other than themselves because over the decades, we've been encouraged to be selfish and self-indulgent.
That's my view anyway.