"And there's a mobile phone-"
"A what?" I say.
"A phone", he says. "It's cordless. You can use it anywhere. Outside the house, anywhere. It'll be in your handbag. Make sure you take it with you if you go out."
She would be well aware of what a phone is and what it does from before she lost her memory - and phones are pretty intuitive these days. I think the author did a reasonable job of putting the mobile phone into the realms of plausibility.