Is there an easier way to turn wifi on and off on iOS?
You don't specify the model of iPhone you have, but the Control Centre is definitely the easiest way to toggle many functions on/off.

Typically, to access Control Centre you would swipe up from the bottom of the screen. If you have an iPhone X you need to swipe down from the top right of the screen instead.

You can configure the Control Centre by going to Settings > Control Centre. If you're on iOS 11 you have a lot more options available to you and can even select what functions you want available from the Control Centre.

Below is a screenshot of how I currently have my Control Centre configured:



As you can see, by accessing the Control Centre you can instantly tap on the Wi-Fi toggle to switch it on/off. The Control Centre also give you fast access to Bluetooth, Airplane Mode, etc.