Phones do not have "hooks" anymore. In the old days, when a phone was not being used, its receiver (the part that goes against your face) would hang on a metal bracket. The weight of the receiver would pull the bracket down and hang up the phone. So, a phone that's "ringing off the hook" means it keeps ringing so much or so often, that it falls off the hook.

Hi, The phrase "My phone is ringing off the hook" means that it is ringing constantly (i.e. you are receiving a lot of calls). I hope this helps. Dean

It means getting a lot of phone calls, especially if the call happen while already on the phone. It references how old house phones would be on a hook when not in use.