Remember that your google account is not only your email. It is everything linked to your google account, form mobile devices, to various applications you are using.
So, you could get locked out due to some app or add-on misbehaving. like Receiving, deleting, or downloading large amount of messages in a short period of time. Or simultaneously logged in/sync synchronizing Gmail on many devices and/or clients and/or locations.
I would say most possible scenario for your case is mis-typing your password in an application that would keep trying to login (particularly if you are in the middle of developing this app) for example.
A second possibility is if you have just changed your password with a new clever one that made sense at the time but next morning you are not sure if it has a “.” or “_” in it or none at all. Even though you use your account all the time I assume you are like the rest of us: you do not logout of your account every time you use it and you do not really type in your password all the time.
Now that I addressed the scenarios part of your question, allow me to address the bigger picture here:
You are looking at the problem backwards: your phone is the most important, physical authentication item in your life. If it is lost or stolen AND you didn’t have it locked/password protected then the person who has your phone (until you remotely wipe it and block it) basically owns your life and there is nothing you can do about it. You can lookup many articles on the subject. Not to mention that if someone used your phone then they already have access to your email accounts because I assume you have them auto-logged in for your phone to check new emails etc.
Conclusion: having your phone number for recovery does not compromise your security because if someone has access to your unlocked phone they already have access to your accounts, no need for recovery phone number…. If your phone is locked, then they have nothing.
A couple of notes I would like to add:
1) The phrases “use password manager”(as in a program/service that saves your passwords) and “proper security practices” (in my opinion) do not fit in the same sentence. If you use a password manager you have already compromised your security
2) If you are already use 2FA then you already provided the phone number.