The risk is higher on the phone. Because you don't get the response to your speech on the phone visually, which will directly tell you that you are not understood by the person on the phone. That's put you in panic. The responsible mental blocks are self-expression deficit and being judged. My suggestion: Try first speaking to your friends on the phone by letting him know earlier. That will decrease the effect of mental blocks. You will talk with airflow, just by letting air for 1 or 2 second from the mouth before speech. Talk for 6 seconds and stop. Your friend will give you feed back: I understand you perfectly. Go on this cycle for 10 times. You should feel yourself better, if you can use airflow well and become fluent. For a long term success, see my other posts about reinforcing positive and weakening negative feelings by EMDR.