I've had an Epson Workforce 630 All-in-one printer for a couple years now.

If someone is on the phone, I can't print. The printer's screen reads an error message that the phone is off the hook, with two choices at the bottom indicating send or receive. I have faxed on this machine minimally but I don't think I've tried to receive before. I've had trouble getting the fax functions to work.

I've looked through the manual and googled. It's hooked up like the manual says. And I do have a DSL filter on the line.

Have you phoned Epson for tech support?

That is relatively common behavior for multi-function devices. You might consider disconnecting the phone line from the Epson except when you want to send or receive faxes.