Why would the screen not Display anything.

Sounds like he’ll need a screen replacement. LCD had been damaged. You can either order a kit on ifixit and DIY the repair or take it to a good local repair shop. It uses the same display as the iPhone 8 which is nice.

Edit: just be aware that after either repair, you may get a message that says “apple is unable to verify this is a genuine display”. This is nothing to be too concerned about. A lot of reputable repair shops will often use high quality aftermarket parts as apple doesn’t sell parts to anyone. It will also lose its liquid resistance. Apple added that message to deter those who would buy iPhones from their stores, swap the parts for cheap aftermarket ones, return it for a refund, then sell the OEM parts.