Is there still integrated login on the iPhone for Google, Facebook, and Twitter?
Yes, Apple has removed the Facebook and Twitter integration starting with iOS 11.

Google integration has never been available in iOS in the manner similar to how Facebook and Twitter was. However, it has been always possible to add a Google account on your iPhone to access Mail, Contacts and Notes within the 1st party apps. The option can be found Passwords &amp; Accounts section of iOS Settings app.