As a professional, you are on the phone a lot to suppliers, clients, colleagues and so on. You speak to all of them without being able to see them. As a result, you miss a crucial part of the communication: their facial expression and body language. You can still sense the nuances in your native language but can you also do that in German? Or are you seized by a fear of speaking in that situation?
Could this be for you?
You already have command of German to an intermediary level. That means you already speak German reasonably effortlessly in familiar situations. You are OK with face-to-face conversations but you don’t feel confident talking to someone on the phone. Then fixing those arrangements suddenly becomes a lot more difficult.