If you describe the process of building a phone in fantasy terms you can see that it kind of is a sort of dark magic.

Thousands of slaves spend their days digging up the earth to produce a tiny quantity of rare metals and elements. These are etched into intricate runes by automatons, themselves built by scholars and technicians that have spent their lives studying these secrets.

Legions of our brightest minds spend their days writing incantations that allow these rune devices to perform new tasks, and sometimes, subtly alter the way those who use them think so they spend more time looking at them. Sometimes, people stare too long at them and lose their grip on reality.

I really believe if you described what smart phones are to a medieval peasant they think you lived in a horrible and profane empire under the control of dark wizards that create lovecratian madness runes. And they'd be right.