Suggest Treatment For Speech Disorder

Dear Sir, I got your reference through internet. I am 29 years old male. I need your help in treating my speech defect. In routine life, I speak normally. But this problem of strammaring starts when I am under any kind of mental pressure. Due to nervousness or performance anxiety, I am unable to speak. I struggle for words. I think it is a psychological problem but dont have any idea how to cure it. This speech defect is interfering with my professional work. I have difficulty communicating with clients on telephone, making business presentations, etc. It makes me feel tense and lacking in confidence. Kindly guide me further. Thanks, Abhishek