Can I block out a device from connecting to my Wi-Fi?

My dad's iPhone keeps shutting my internet down when he leaves/enters the house with it. It really screws me over when playing an online game. Is there a way that I can block his device out of our Wi-Fi? He is a very old fashioned person and doesn't know that the iPhone can do more than call/text so he won't notice at all if block him out.

Added (1). I play online games, he does not.

Haha… Old fashined person knows how to play online games, but doesn't know that his phone an do more than call/text. You are contradicting yourself. BTW, why does he have an iPhone if he doesn't know what his phone can do? And even if he has it, why can't the Wi-Fi on the phone be turned off?

I don't know what are you trying to achieve here. But anyways, ever heard of MAC filtering technique? Use it if you really want to block any device from connecting to your Wi-Fi

It does seem odd that an iphone that might start connecting with the house Wi-Fi network would knock you off. It does sound like your house router is set up so it can have only one device connected at a time. It is possible to do that. You could block his MAC address but that would anger him when he tried to use the Wi-Fi. Go into the router config page (192.168.x.y for your router) and make sure that you have enough IP addresses (usually something like up to 192.168.1.100)
As another thing to try, change the channel that your router uses.