Lost iPhone

You can't.

Unless you had Settings > iCloud > Find My enabled on it then there isn't any way to try and locate it. If you did have it enabled you could try locating it either via http://www.icloud.com on a computer or Find My app on another iOS device - but that will only work if it's connected to a network

If you think that it was stolen you should report it to the police (to get its serial number : Find the serial number of your Apple product - Apple Support). You should also change your iTunes account password, your email account passwords, and any passwords that you'd stored on websites/emails/notes etc., and if it was a cellular model also contact your carrier.

And see : If your iPhone, iPad, or iPod touch is lost or stolen

See if anything here helps. 

https://www.imyfone.com/ios-data-erase/9-tips-to-fix-there-was-an-error-connecting-to-the-apple-id-server/

https://appletoolbox.com/error-connecting-apple-id-verification-failed-how-to-fix/

https://macreports.com/verification-failed-there-was-an-error-connecting-to-the-apple-id-server-fix/

https://appuals.com/fix-verification-failed-there-was-an-error-connecting-to-apple-id-server/

https://errorcodespro.com/there-was-an-error-connecting-to-the-apple-id-server/

https://search.yahoo.com/search?ei=utf-8&fr=aaplw&p=Verification+Failed%22+There+was+an+error+connecting+to+the+Apple+ID+server

App Store, iTunes Store, or other Apple services - If you can't connect

Some other things you can try. Do you have access to another WiFi network where you can try? That has worked for several people.

Try a restart.

Restart your iPhone, iPad, or iPod touch         

Try a forced restart.

Reset Device.      

If necessary

Hard reset.        

Do a backup and try a factory reset. Then restore from your backup.

Restore to Factory setting.      

Backup - Restore your device from an iCloud or iTunes backup.      

Also see

Find My Phone - Lock and track your device using Lost Mode.