Wifi turns off when iPhone is locked.

How do you know the WiFi switches off when locked?

There are a couple of reasons why your iPhone might be behaving this way:

• Battery Saving: By default, iPhones will sometimes turn off Wi-Fi to conserve battery when the phone is locked and not in use. This is especially true if it's not plugged in.
• Wi-Fi Assist: This is a feature on iPhones that automatically switches to cellular data when the Wi-Fi connection is weak or unstable. This can be helpful, but it can also lead to your phone switching off Wi-Fi entirely when locked if it thinks the connection is poor.

Here are some things you can try to fix it:

• Keep your iPhone plugged in: If your iPhone is plugged in, Wi-Fi is less likely to be turned off to save battery.
• Turn off Wi-Fi Assist: Go to Settings -> Cellular -> Wi-Fi Assist and toggle it off. This will prevent your phone from switching to cellular data when the Wi-Fi is weak.
• Check your router settings: Some routers are configured to disconnect devices that are idle for extended periods. This could be happening with your iPhone when it's locked. Try restarting your router or looking for settings related to idle device disconnection.