I have the opposite problem where I talk so fast people ask me to stop and slow down before repeating myself.

When you are answering the phone is the type of situation where you are maybe typing away and doing something else? So when you answer the phone your mind might still be on what you are working on besides the time of the day.

As I type this, I wonder if I used to have this problem because I now have a habit where when my phone rings I put my hand on it, look at the time and then answer. I've been doing that for years now. Not saying that would work for you but I guess I make it a point to stop and check so I don't make this mistake.

I know that if I make that first mistake on time it makes me trip over the rest of my words the rest of the conversation and stopping to think before I answer has helped me to stop making that first mistake.