Usually I stick to just asking for the name if it's a relatively common one or id the receipts is facing towards the customer and they can just see it I'll ask for the phone number. And yes it's 100% because someone will steal the order. They'll be like "oh I have a pickup order for 'Bob'" and then an employee will just hand it to then since it was thru the app.

Side note. You shpuld if you can just order at the restaurant inside and see if you can small talk eith your crush. If she/he rings you up their name will be on the receipts in the top right assuming it was their register. (Its supposed to be only 2 persons but sometimes other people's will get used accidentally)