Till now you can only say both “OK Google” and “Hey Google” to Google Home and it responds flawlessly. And till now Google assistant on your Android phone only answers to “OK Google.”, but wait the “Hey Google.” command is now working on phones too.
According to a Androidpolice.com article it is working on samsung S7 and S8 both but not with Nokia 8 till now.
Support for the Hey Google command is not yet universal.
After an update to google assistant, you will get a notification saying as much, though you can also check the Google Play Store for an update to the Google app. From there, you can train Google Assistant to listen for your voice when you say either “OK Google” or “Hey Google.”