Having realized that I was still using app-specific passwords for my Gmail account on my devices, I just switched to OAuth. I had a look at my account permissions which showed the following:
The bottom item was created just now after re-adding my Google account in the iOS System Settings using OAuth.
But what's the iPhone item?
When I click on it, the sidebar says my iPhone has full access to my Google account and it was authorized on April 21st. That's not too long ago, but unfortunately I can't remember what I did on that day.
According to the "Learn more" link, some apps (e.g. some Google apps) might have full access. It also specifically mentions iPhones and Android phones, but it does not say why they would appear here and what causes them to show up.
What is this item, and why did it appear?
Is it safe to revoke access?
After all, I have properly set up access for iOS now.