Your use of "bloke" implies you're in the UK, so perhaps it's just manners... But as someone who has worked in a large, multi-cultural office in the US, it is definitely a cultural thing. There are some people that have no problem chatting on the phone at full volume, in an echo-y stall, while audibly shitting. And I mean audibly lol.
I have had one experience where I was sitting in the middle stall, of three, between two people who were having a full-on conversation back and forth over me. I kept like clearing my throat just in case maybe they didn't realize someone was there... Nope, they just didn't care lol.
Just the thought of behaving like that is mortifying to me lol, especially in an office where I have to then interact with those people...
There are some people that have no problem chatting on the phone at full volume, in an echo-y stall, while audibly shitting. And I mean audibly lol.
I experienced that in New Jersey once. A man was speaking Spanish, presumably while on the phone. And he was very audibly taking a shit. He even continued talking while straining to push the poop out.
I kind of get that. But I still feel it would be incredibly rude if someone called me and I could hear them on the shitter. But that's my personal sensibility.