Student or Learner
"Has John left already? Not yet. He is speaking with his boss."
Is "speak with'' more formal than "talk with" so it's appropriate when having a conversation with superiors?
In that context, I see no difference between:
He's talking to his boss.
He's speaking to his boss.
He's talking with his boss.
He's speaking with is boss.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.