I haven't looked through that thread as it's too long, but if people are willingly posting their real data publicly then there's probably not that much you can do about that. Most people that do probably don't care, though. I know people should be careful with what they post online, but us bitcoiners seem to be extra careful, but for the vast majority of people they're seemingly happy to have public Instagrams and accept any facebook friends request they get and so forth.
You can just use a throwaway pay as you go sim. It's probably a good idea to have one because there are many other sites that require them that you may not want to give your personal number to. I know most email providers now require a phone number so you'll probably need one even if you want to create a throwaway address with them. I don't think telegram displays your hone number to others either. I also believe you can use telegram on your computer like skype and so on.