Buying prescription food in store without a physical script on hand?

Hey all,

I've been doing some digging around and found out that in order to buy prescription food in store I would have to bring a script to the Banfield so that they can give me a medcard to bring to the cashier. I can't find any info on if this would work if I don't have a printed prescription on hand? Can I still go to the Banfield so that they can verify with my vet via a phone call?