Lost IPhone

If find my phone is enabled on the lost phone, you can go to www.icloud.com

Sign in with your apple ID and go to the find my phone section.

Also see:

Follow the steps:

What to do if your iphone is lost or stolen.

https://support.apple.com/en-gb/HT201472

Go on any device or computer and sign onto icloud.com/find. You should not need 2FA .

If you do not have any other apple device to receive 2FA codes make sure to type in

icloud.com/find in the URL and you will not need 2FA

If you just type in icloud.com it will want verification.