unable to join network iphone this network is operating on wi-fi channels in use by several other nearby networks

You get that message because you tapped the Wi-Fi icon in Control Center. 

So the Wi-Fi icon turn to 'white' -> Wi-Fi Is deactivated.

The current Wi-Fi network and others nearby will be disconneted until tommorow.

Wi-Fi wil continue to be available for AirDrop, Personal Hotspot, and location accuracy

Your iPhone is disconnecting nearby Wi-Fi until tomorrow because you tapped the Wi-Fi button in Control Center. The main purpose of this pop-up is to clarify that tapping the Wi-Fi button in Control Center doesn’t completely turn off Wi-Fi — it only disconnects you from nearby networks.

To activate the Wi-Fi again, tap OK and tap on the 'white' Wi-Fi icon, it will be turn on to 'blue' again.

And you will have Wi-Fi connection again.

To turn Wi-Fi Off or On, go to -> Settings -> Wi-Fi.