Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
When connecting up a fax hookup, you need to plug the phone line (from the phone wall jack, the phone service, the VoIP phone box, or similarly) to the 'LINE' port on the machine, *not* the 'PHONE' port. Problems such as those you report can result if you get this hookup detail wrong.
Then the 'PHONE' port on the faxing device, gets hooked up, with another phone cable altogether, to whatever other device(s) is/are on the line with the fax.
Then you make sure, by using Speakerphone mode on your phone (if there is one on the line with the faxing device) that you have a dial tone, and that you can hang up the line also.
If there's a problem after that, you need a review in some detail, of what your phone service type is (regular/landline/POTS, vs. digital/UVerse/Comcast/VoIP/Vonage/MagicJack/etc.) and what devices you have on the line exactly. Also you might need to swap out a cable (defective phone cables are rare but do happen.)
Let me know what happens, and what you think, and how things are hooked up, please. Thanks.