From reading that, I can tell that you are capable of stutter free phone calls, the environment has caused you to stumble and now you’re anxious and in your head about everything. If possible, try set up a new ‘office’ at home. Move about the furniture, buy something new, paint, etc. maybe a change in environment could make you start fresh. Another thing. What hours to do you work? Do you have enough time to do anything before work? If you do, maybe go out for a walk, exercise, or anything to help improve your mood. Lastly, do you have introduction script ie “hi, name here, how can I help?” ?. Maybe try switch that up, play about with other words. I personally feel that the start of a phone call sets the tone. If you’re confident at the start then you’ll be more confident throughout (personal experience). I worked in a call center a couple years ago for just over a year. I did surprisingly well up until Covid and then working from home started. I was really excited about it at the start but it quickly became awful. The exact same thing happened to me and I was down for quite a while. I did all everything I’ve just stated above and it might help you out. Good luck and you’ll 100% get through it. I think of it as a rollercoaster, once you’ve reached the bottom, you can only go back up