My iPhone screen is broken, I’m trying to log out from iCloud but I can’t, is there anyway I can do it from the computer?

See item 6 here.

If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support

The first thing you must do is make an appointment at your local Apple Store for an evaluation of the damage and explanation of your options. If you are logged into iCloud from your computer, you can sign out there, but I'm not sure if this will log you out on the phone - my guess is probably not?