What should I enter as my phone number? It won't accept my Korean number and I no longer have a US number.

You can just leave it blank. They only want that to contact you about the status of your returns, but as long as your email address is good that will be the primary way they contact you.

If you do not have a phone number you can enter a "fake" number so that you may continue.  Select your area code then use the number 555-5555 this will allow you to move forward in preparing your tax return.