Hello abarbs, and welcome to the HP Forums, I hope you enjoy your experience!
I would love to try and help with your fax output issue, but I would like a little more information as well.
1. Have you run a fax test? What is the outcome of the fax test? You can find the fax test details and how to print a fax test here: Using the Fax Diagnostics Test.
2. Can the printer print a basic stand-alone copy? You can follow this document on Copying a Multipage Original.
3. Who is your phone provider? Are you using a VOIP telephone service?
4. Is the fax machine connected directly to a telephone jack in the wall or into a modem or router?
5. Which operating system are you using.? Also, if you're using Windows, please include whether your operating system is 32-bit or 64-bit. You can use the following documents to determine your computers operating information:
Mac OS X: How Do I Find Which Mac OS X Version Is on My Computer?
Which Windows operating system am I running?
Is the Windows Version on My Computer 32-bit or 64-bit?
As well as gathering all of that information, I would suggest following through with this document on Receiving a Fax to ensure the fax settings are correctly set up to recieve a fax successfully.
Another helpful document to run through would be this one: Cannot Send or Receive Faxes. The troubleshooting steps listed here should help resolve the issue.
Good luck and please let me know the results of your troubleshooting steps. Thank you for posting on the HP Forums!