Locating an iPhone from my I phone

If you had Family Sharing an location sharing set up, see the following from Share your location with your family - Apple Support

Help find a missing device

If you turned on Find My for your device and you share your location with your Family Sharing group, your family can help you locate your device if it goes missing. Family members can:

• See the location and online or offline status of your device.
• Play a sound on your missing device to help you find it.
• Put your device in Lost Mode if it was already set up with a passcode.
• Remotely erase a device.

Learn more about how to use the Find My app

If you don't share your location, family members can’t access location information about your device. However, family members can still help you. They can check your missing device's online or offline status, play a sound on the device, put the device in Lost Mode, or remotely erase the device.

If that wasn't set up, use any internet browser and log into www.icloud.com/find using his Apple ID and password.

Also see the following Apple articles for information about lost or stolen iPhones or iPads: If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support and

Use the Find My app to locate a missing device or item - Apple Support

Is he a friend?

Learn how to use the Find My app to share your location with friends and family members. You can even set up location-based notifications, so that you know if someone left a location or just arrived home.  Refer to the document:

Find friends and share your location with Find My - Find people and share your location with Find My - Apple Support