The Wastes of Keldora by Alex Raizman
Summoned to another world where gods and monsters roam, Julian continues his streak of bad luck. Rather than touching the Godcore directly, he let his smartphone absorb it. Now, he's got to figure out how to make the Godcore and his phone work together to help the people who summoned him survive their upcoming annihilation by the mad God of Chains.
He's going to have to innovate his way out of his bad luck. Good thing Julian has a plan - he's going to build a factory in a medieval world.