You can only enter a U.S. phone number in this field (Contact Phone under Personal Interview). It will not accept an international phone number.
The IRS asks for this phone number in case they want to contact you about your return (very uncommon). Even if you entered an international number on a paper return, the IRS would not call it - they will only use U.S. numbers.
If leaving this field blank prevents you from efiling, you can either enter a working U.S. number you are associated with (e.g. a relative's phone number), a working dummy number (e.g. 800-555-1212 - Toll-free directory assistance), or enter an obviously non-working number (e.g. 888-888-8888).
