I’ve got two factor authentication. What if I loose my phone and I try to use “find my phone” from my computer?

When you log in, you will get the 2FA screen. But, there is a link to go to Find iPhone without it. nSee the picture below:

Glad it helped.

I would also suggest that you set up other trusted devices or numbers. I have my iPhone, iPad and Mac as trusted devices. I have my work landline (doesn't do so much good now!) and my Google Voice numbers as trusted numbers. I'm unlikely to be unable to get a 2FA code. Belt & braces.

You can use any internet browser and log into www.icloud.com/find without needing a two-factor code.

You can also log into www.icloud.com (without the /find), ignore the request for a code and click the Quick Access to Find My button instead.