My personal take is that having phone conversations at normal speaker volume is fine because people also talk amongst each other in public and there is no substantial difference, but watching videos or even listening to music on loud speaker is not okay because it's a public nuisance.

However, it seems that the cultural norms differ a lot, I've heard of people who disapprove of almost everything and don't have much sympathy for them. Politeness goes both ways, and in my opinion using that app is impolite, too.

There is a substantial difference between people talking amongst themselves and one person on a phone.

Humans are social animals, we tune out conversations easily. Half conversations are just one interrupting, attention-grabbing … jarring start … … after … … … … another. It’s a series of unpredictable spontaneous one-sided outbursts, behaviours that otherwise belong to disturbed individuals.

Listening to people in the phone is inherently more annoying, backed by decent research IIRC.

Phone speakers are tinny and sharp and I find them a lot more annoying.