How to find where's my lost iPhone?

FindMy is the only method available to you.

You can access FindMy either from another Apple device you own or thru a browser.

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

https://www.icloud.com/find

If Find My is offline or not working - Apple Support

Also see this checklist of tasks:

If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support

BEWARE:

Criminals who find your phone may phish you in the future.

They usually claim to be from Apple (or the police) and direct you to a site for you to enter your device passcode and/or AppleID credentials.

These are NEVER legitimate.

Apple NEVER does this.

It’s ONLY the criminals attempting to break into your phone AND takeover your AppleID.

Do NOT reply and NEVER follow any links these messages might contain.

No legitimate entity will EVER ask for your passcode or password.

Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support