Short answer: no. A phone number alone won’t let you track an iPhone. Services that claim this are typically scams or require access to the device to set up location sharing.
Use one of these legitimate options instead (the iPhone owner must enable sharing on their device):
- Apple Find My (best): On their iPhone, Settings > [name] > Find My > Share My Location. Then in Find My > People > Start Sharing Location > select you. Or set up Family Sharing (Settings > [name] > Family) and enable Location Sharing.
- Messages: Open your conversation > tap their name > Info > Share My Location > Share Indefinitely.
- Google Maps: Google Maps > profile photo > Location sharing > Share.
- Carrier family locator: Available on some family plans after enrolling lines.
For your own lost iPhone, sign in to Find Devices - Apple iCloud or use the Find My app to locate, play a sound, or mark as lost.