I think I read once that someone put just any old US number in there, such as an IRS phone number. Unless they actually use that number to validate your account.
I recently created an IRS account without the need for a US phone number. Not sure if you can file directly from the account but is great to see the history and status of past and current tax returns, even paper returns which just seem to shoot off into a black void with no feedback unless they think you made an error or didn't send them enough money. This happened to me on my federal return (missing documents) and Louisiana State return (wanted more money) for 2020.