It's easy to freak out if you're staring at the phone waiting for it to do something. So, first take a deep breath and a calm down. First, double check that you do have the right time and day just in case (you're probably fine, but it happens). Then, take a moment and put things in perspective. It's not that they changed their minds or don't want to talk to you. When you interview in person someone is usually there to tell them that someone had arrived for an appointment and to give them some warning to wrap up whatever they are working on. That doesn't happen when the appointment is for a phone call so it's easy for someone to lose track of time in the midst of work or get backed up. That is most likely what is happening.