Yes, you can retrieve your prescription, but you cannot call your optometrist to get it, instead you should go there yourself to get it. Optometrist will show you the copy of your prescription until you provide him the evidence that you have done eye exam right here before. You'd better go and get it as short time as possible.
Make sure your prescription is still valid. Every optician will keep the customer's information on file. So you can retrieve your prescription from your optometrist as long as you go back there and show him the reciept in order to let him know that you've done an eye exam before there. Then he will write down the prescription to you.