I'm also, like, 90% sure that when you are using your custom domain on Google, as a business user, the "recover my email via phone number" option goes away, because you are your own "administrator" and if your "users" lose their password they just have to go to you.
(Which closes that gaping hole in your email security.)
I'm not using the "Google Apps" part of their services, i'm just using their "domains" offering at domains.google.com
They can be the same thing if you want, but they don't have to be. You can use an externally hosted domain with google apps, and you can use Google domains without "google apps" (like I do).
Also, as of somewhat recently, I believe you can disable "recover by phone" as an option if you want for any google account.
(Which closes that gaping hole in your email security.)