I don't know what country you are in but, in the US, they have to provide it if you ask (not sure if it must be free of charge), but most places just give you a copy if you ask. Generally, it is good for 2 years from date of eye exam. They probably will NOT give it over the phone as the risk of an error is pretty high. When you get it, before leaving, look at it and make sure you can read/understand it; ask if necessary.
In the US, doctors have to give you the copy of your prescription if you can provide the evidence that you have done the eye exam right there before. But I am not sure if it is free of charge. Make sure you can read and understand the prescription before leaving the office. Just get the prescription by yourself, not to simply call on phones.