It’s just on work phones, they can do what they like on their personal phones of course. However, if they are discussing anything business related they’ll be fired and could be barred from working in the industry altogether.

HSBC etc completely lock down Teams etc, there is no private anything, it’s all monitored as long as its on their devices and accounts.

Traders and other front office staff will have every single phonecall, email, IM, voice chat, and video call monitored and stored for something like 7yrs.