I'm not sure I agree with that answer. I just tried signing up to test this and after submitting was asked for a phone number to verify. The first form didn't require a phone but after that it redirected to a page with a link to https://support.google.com/accounts/answer/114129?hl=en&ctx=... that referencing GSuite verification.

I feel like this is a very recent change; I've definitely created "burner" gmail accounts in the past and I don't remember providing my cell phone number.

Yep, same here. For me it had to be at least 5 years ago.

Yes, but they will link you to a mobile number and then require that you confirm your number on grounds that they cannot identify you from your login. Gmail did not have my number confirmed until I moved and they locked me out of my email, despite answering all security questions. Theory and practice can be very different.

You are right. Many bad assumptions were made by me today.