Google highlights the importance of linking a phone to an account when it comes to fighting hijacking attempts from automated attempts from bots, phishing, and targeted attacks. Study shows that where a Google account was linked to a phone, the takeover prevention rates went up as much as 100% in the case of automated bots, as high as 99% with run-of-the-mill phishing and up to 90% with targeted attacks. The same vulnerability exists for targeted attacks because phishing can trick you into revealing any additional identifying information.
Source: https://www.bleepingcomputer.com/news/security/google-wants-your-phone-to-protect-against-account-takeover-attacks/