How is me talking to a friend in great distress something I should hide from my partner? Actually, if that did happen, I'd almost certainly tell them so I could get their advice as to how to respond.
But okay, If someone did message me, "please don't share this with anyone, but..." then of course I would respect that. I was a trained counsellor in a previous life, so I understand that aspect. It's never happened to me though. There's still nothing to stop me saying to my partner , "ah, sorry, something has come up that I need to deal with, that I've been asked to keep private, excuse me for a minute'.
However, in my original post I was referring to doing things on my phone that I was hiding from my partner, and I was thinking of things like having an affair or looking at porn or gambling or whatever it was that I wouldn't want them to see as if been hiding it from them.
I was not saying " no one can talk to their friends about sensitive and delicate subjects in their phones as that's wrong". I am talking about me and my relationship with my phone and my partner. I did so as I thought it might help the OP who a lot of people seemed to be having a go at. From what I can tell (and yes it's "just" her side, he sounds like someone she should get the hell away from as quickly as possible.