There are two types of pins:
1) The personal 5-digit filing pin that the IRS no longer issues or uses, but will still honor the pin that was used in 2018 if you know what it was. Now the IRS only used the 2018 AGI for filing identification. The 5 digit pin is also used as a electronic signature to sign yiur e-filed return.
2) The Identity Protection (IP Pin) which is a 6-digit pin issued each year by the IRS that the IRS mails to you each year that it is needed. It changes every year so you cannot use last years IP Pin.
If the IP Pin required by the IRS you cannot e-file without the IP PIN.
If you lost or did not receive it then your only options are to:
1) use the IP PIN recovery site:
https://www.irs.gov/identity-theft-fraud-scams/retrieve-your-ip-pin
2) Wait for the phone service to return.
Presently, because of the Corona virus shutdown, the IRS is not taking calls.
3) Print and mail file. (The IRS is currently only storing incoming mail until the IRS reopens).
https://www.irs.gov/newsroom/irs-operations-during-covid-19-mission-critical-functions-continue