It's direct speech! When you talk to someone through phone, there is this instant fear of embarassing yourself, because the person you're talking to is paying all of his/hers attention to you. If you would speak with him/her in person in a party for example then it would be easier, because the person might be a bit distracted. It's always easier to start speaking when you're not in the middle of attention, but when you are, let's say a group of people asks you to repeat that sentence you said perfecly, but this time you can't.