I doubt that is correct about the USA phone number. If you enter a UK name and address into your seller application then it would surely allow a UK phone number. Amazon deal with sellers all over the world. I have always had an Australian phone number on my account even though I actually use a US-based LLC as the registered business on Amazon.
Re the EIN number: yes, that may well be correct about talking on the phone to the IRS. They have an International EIN Hotline just for international applicants. When I called it (over 5 years ago), it was a very quick and easy process and the staff were very helpful. Just explain your situation to them and they’ll tell you exactly what you need to do. It’s not 24/7 so check the operating hours before calling.
Re the tax stuff: it’s best to get advice from other UK members or your accountant on this to be sure, but unless the UK/US tax treaty is very different to the Australian/US one, I would doubt that there’ll be any tax withheld or paid in the USA.