You can leave this phone "off the hook," but...
you can't leave this phone "off the hook."
I would be appreciative if you give it your full consideration before giving an answer to the question, especially if you are not sure about it.
"“My cell phone was ringing off the hook,” said McCallen, the president of the MSU Alumni Club of Tampa Bay, Fla., and an MSU alumna. “I got a lot of text messages, and I had a lot of e-mails asking about tickets. … Everyone’s really excited to have the team down here.”
Given above is the context where it's used figuratively. Once again it's got nothing to do with "leaving off the hook."