You can create an account even without an invite. If you give it access to your contacts, your friends will get a notification to invite you, if they have an invite to give. Once you get an invite, your account will be activated, and you can use Clubhouse.

This is how I got in, through a friend I hadn't talked to in a while.

That’s an interesting way to scrape people’s connections and phone numbers.

It's been done before. I consider it a passive dark pattern.