Phobia of telephone talking. I do

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I don't have the same problem with my friends or family.
But when I need to call someone whom I don't know or don't know well enough, I always making a conversation(one-sided) in my head before call which probably makes me sound very robotic during a conversation

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When I was an intern in some office I had to talk on the phone all the time (even though I tried to avoid it with every possibility I got) and when I've talked to the clients on the phone I hanged up as soon as they started asking me questions to which I didn't know the answer

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Right now I need to call my teacher but instead of calling him I'm writing this

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Does anyone of you have the same problem?
Edit: my English is a mess

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