This unfortunately is useless. Account recovery will still allow the hacker to use the phone number that has just been swaped to logon to the email. The weakest link is what matters and in this case you are just putting a bigger door lock on the front door while leaving your back door open.
Once you've configured a security key on a Google account, it's entirely possible to remove phone-number based account recovery -- and strongly recommended for at-risk users. See step 21 et seq. in the Tech Solidarity security guide for people working on political campaigns:
For no particular reason, Google does require you to temporarily configure phone-number based recovery while configuring other 2FA options -- but once they're set up, you don't need the phone number anymore.
