I know the situation you are in as I am learning Spanish and have similar problems.
You probably automatically freeze when you speak on the phone as you associate it with bad English speaking experiences.
A good idea is to learn the basics of telephone conversation, as this will give you more actual skills and will increase your confidence. The links that were posted in an earlier post are very good. Start with these and see if this helps. Remember to do some role plays with the phrases used. Say the phrases out loud just as you would as if you were on the telephone.
It seems that you also need to practice more. I think that you need a more relaxed environment, and this can be done with an English tutor. Take things slowly and work on the basics, which will increase your confidence little by little.
If you need to take an English course -
improve spoken EnglishGood luck with your learning.