Restaurants have thin enough margins already. They aren't turning away a customer for not bringing a phone. There's one tiny burger place just around the corner from me that's delivery/pickup only, not even a QR code, but they have a sign outside saying 10€ combos and they're 15€ on the website... I just asked them. They have very good halloumi burgers and perfectly cooked fries. They were happy to accept my cash, too.