How do I find my iPhone from someone else’s iPhone?

According to: Locate a lost or stolen device - Apple Support

"If a friend's device is missing

You can help a friend find their device if it's missing and has Find My [device] turned on:

1. Open the Find My app.
2. Choose the Me tab.
3. Select Help a Friend.
4. Have your friend sign in to iCloud with the Apple ID they're signed in with on their missing device."

Open Find my iPhone on their device. Sign out of their account and sign into your Apple account. If your phone is find my iPhone enabled then you will be able to locate it.

i hope this helps!