It would be helpful to understand what you are going to therapy for. Have you established goals with your therapist for what you want to accomplish? If writing somethings down help you to speak, then maybe writing a path to your goal will help you even more. It's just an idea.

Is it a situation where you are shy? Tongue-tied? Embarrassed? Not comfortable? Memories too painful? Low self-esteem? There are several meditation apps available that might help you, including self-hypnosis. You can work on opening up and speaking this way. Your T might be able to help with some of these tools as well.