phone number is now required for google account?

Nobody has claimed this yet.

I've followed from here:
https://github.com/SchoolIdolTomodachi/SchoolIdolAPI/wiki/How-to-install-Japanese-apps%3F
and to be surprised, it asks for phone number verification even before asking further details (eg. payment)

What should I put? I don't have Japanese phone number (of course).

If you say putting my own number is fine, my number is already linked to my main Google account which also linked to a few payment methods like VISA direct debit. CelcomPay Billing and HotlinkPay.

I'm using tunnelbear vpn as the page suggested (and already logged out of any accounts before turning on vpn) and I was trying to create the account with that steps given on page.

Not only LLSIF, I also want to download a few other apps like Divine Gate...

Start with the linked wiki page and review the account-creation steps against the reported Google phone-verification prompt. Confirm the current guidance for users without a Japanese number, then update the page so the expected action and limitations are clear.

Written by the indexing model from the issue text.