According to the iPhone Life website, there are a number of steps that can be followed to find your lost iPhone and you can also find someone else’s iPhone.
Enable Find My Network and you’ll need to enable Find My Network, by enabling it you can misplace your device for up to 24 hours even if it’s turned off.
If you have already enabled Find My on your iPhone, Find My Network can be enabled by default after upgrading to iOS 15.
If you have an iPhone on hand and want to make sure Find My Network is enabled, open Settings on your iPhone, and tap your Apple ID at the top.
Select “Find My” and then click on “Find My iPhone”, then you will see the option to enable Find My Network.
You’ll also notice that Send Last Location is toggled on which is another useful feature to enable. This will send your device’s last known location to Apple if the battery is low.
Once you enable Find My Network, you’ll see a message the next time you turn off your device. This simply reminds you that your device can still be located even if it is turned off.
How to find a lost iPhone other than your phone
Open the Find My app on your iPhone.
Select Me from the options at the bottom of the screen.
Click Help a Friend at the bottom, and this will open iCloud.com.
Ask your friend to sign in to iCloud with their Apple ID to see their devices.
Select the device you’re looking for, and if the lost device appears to be nearby, you can tap Play audio to help you locate it.
If your lost iPhone is far away, you can click Lost Mode to help protect the data on the phone and automatically turn on Low Power Mode to give you more time to search.