I agree with the Talking to Win recommendation.
Anxiety-Free would also be a powerful one. Conversations like those can be stressful -- having the conversation in a foreign language is much more so. The more relaxed you are about phone conversations, the more easily you can understand the other person and remember the words you know.
Here are some other ideas:
Self-esteem Supercharger
Positive Relationships / Instantaneous Personal Magnetism
Belief
New Behavior Generator
Thanks for sharing this issue with us. If you feel comfortable doing so, please let us know how things progress.
Best of luck!
Warmly,
Laura