Maybe I'm different, but I've had the same number for over 15 years. I already know my phone number, I do not need to see it in Self-Serve anymore than it's already displayed.
@stonechucker me too....but.... think of someone managing a family of phone lines. Spouse, child 1, child 2, maybe a parent, etc. Each one of those, as you know, is a separate account by design. So there is possibility of not realizing you're signed into the "wrong" account when doing something. We've seen people accidentally port numbers into the wrong account before, or purchase add-ons on the wrong sign in (less troublesome than the port situation but still inconvenient). I can see how this might be helpful to some.
The interesting one in my case is if I logout of one account and then logint another account I will see details usually the plan summary and the balance of the first account. It has confused me a couple times.