I have seen some videos from Vitaly (a quite famous guy on youtube), where he just asked directly to the girls if they could put their phone numbers on his phone. Do you think these approaches are cool?

I have used it two times so far. The first time got rejected, but the second time i got the girl's phone number and we also had some chatting.

I could put the link from the video here, but as I am a new user on this forum, it is complaining about the URL.

PS: just to you know, I'm still a beginner in this PUA lifestyle, this is why I'm asking to you.

All the best,

Yes, I've done it and it worked. But, unless you have great text game or are really attractive, it won't do much good. A phone number is damn near useless without a connection. Most of the time you won't even get a reply.