> why would I need someone to tell me 'I agree with you', 'go ahead

You might not, but that's just an example where a different style of communication might help some people. It's great that you would be happy without validation, but I can safely say some people do flourish when given it! Lots of people need to be given a bit of confidence, particularly when they are new to a role, and in my experience that's easier over a call.

As another example if I ask people on Slack how busy they are I will often get a different answer compared to calling them and checking in, asking if they need support, particularly if I can hear that they are stressed.

Or while on a text chat someone might say they understand a problem, on a phone call it's much more natural to get them to play it back to you so you can work out when they miss some nuance.