If I already opened an account with a phone number as I don't have a card yet,will I be able to enter the card number once I get one?

A lot of the reward cards you have to to register online ie circle k, Panera and others. I'd advise going into the app online it will most likely answer any questions you have.

I want to understand you will not get a physical card your cell phone will have a barcode that is your card that's at least as for the rewards card now if you're talking about a credit card I have I'm not sure