I see.

Having no experience with call apps on Android I can only speculate that the Verizon app will work just like Hiya does.  It seems as if the Android devices have to let the call ring through long enough for the information to be sent to the app and the app then intervenes and rejects the call.

So I would expect the same from the Verizon app.  It doesn't seem this app doesn't do any kind of switch level blocking.

On iOS the Verizon app works exactly like the third party apps like Hiya, but on iOS they all use the CallKit API which asks the app if the incoming number is in the list, and if it is then the operating system (not the app) blocks the incoming call at the OS level so it never rings.  That is only if that number is not already in your contacts or blocked at the OS level.

If you're trying to block a handful of numbers, use Verizon's system level blocking.  It won't even allow the call to go to your phone.

If you're adding spammers to a growing list, then I guess you might not have much choice.

But don't take my speculation.  Try it out.  I find that the service of identifying caller names is pretty helpful for identifying wanted callers for example a Mechanic that's not in my contacts might correctly identify as "ABC Auto" where I left my car earlier that day.  Almost any spammer spoofs caller ID and I'll get a random name that I don't know and I just assume they're SPAM, don't answer it, and figure they'll leave a messge if they're legit.

Without caller name ID, I was missing some wanted calls because I couldn't tell.

Just my 2 cents.

Good luck.