Exactly the same thing. Absolutely infuriating - there's a flag saying "we are doing this for greater security" but not explaining just how it achieves that. There is an option to enter the email and password of an existing google account. I have done this but it claims it's wrong (I know it's correct). Doing it the other way, as though setting it up from scratch, requires the mobile input as tigerlelly says and I too don't want to give mine out. If as VHG says there's a way around that I'm all ears, but even then still hacked off at youtube for what seems a needless change.
Their "help forum" is cluttered with people voicing various issues about this new system. I want to raise this thing about the mobile number but tigerlelly where did you contact them about this? I can't any contact details anywhere, just as usual FAQs and the forum.