Two-factor authentication when your device is not present What happens when you have two-factor authentication enabled for your account, your iPhone gets stolen or lost and you have to login on e.g. an Android device to activate Find my iPhone and you have no other Apple devices with you?
Is there a way to still get into iCloud to activate Find my iPhone?
Is there a way to still get into iCloud to activate Find my iPhone?

Yes, you can login to iCloud to activate Find My iPhone. You can get a verification code via SMS or voice call on your trusted phone number.
Refer to this Apple Support document:

https://support.apple.com/kb/HT204915


What if I can't access a trusted device or didn't receive a verification code?
If you're signing in and don’t have a trusted device handy that can display verification codes, you can have a code sent to your trusted phone number via text message or an automated phone call instead. Click Didn't Get a Code on the sign in screen and choose to send a code to your trusted phone number.