Actually it's pretty standard to get replacement phones in a plastic bag with no accessories, I got a 5S replacement in a ziplock bag with a piece of A4 paper with some diagnostics data printed on it all in a thin layer of bubble wrap then in an envelope. All standard for Authorized Apple resellers and service centers in Eastern Europe, idk in other parts of the world. I'm guessing an official Apple store doesn't do that.

She didn’t buy an iPhone in a non branded box, it’s how Apple sent the replacement phone.

I thought it was weird when we got the replacement though.

I ve gotten these but never had an issue with any of these phones or iPads.