Been able to talk 95% fluent alone.

Been able to talk 95% fluent alone. What I literally do not get is that I am can say anything really well when I am alone but when I was just on the phone. I could not get a word out and I was struggling to say my own name. I do not understand if I can physically say the word at any point why can I not say it when I am talking to people. How does that make sense? Is this a mental barrier or a social anxiety issue or a mechanical but I cannot see how it is if I can say when I am alone. Thoughts ?