As I understand it, a situational interview is sort of like a behavioral interview, except instead of asking you to tell a story about a past event (behavioral), the interviewer asks how you would handle a hypothetical situation. For example, the interviewer might ask, "How would you respond to a family member expressing anger about a patient's care?" (The behavioral interview equivalent of this might be: "Tell me about a time you had to deal with a family member who was upset with a patient's care.")
To prepare for any interview, you have to inventory your professional strengths (e.g.: efficient, good communicator, clinically competent, etc.) and compartmentalize them in your mind so you can emphasize them throughout the interview. For a situational interview, you need to think about possible scenarios that may arise in the job you're interviewing for, and then "plug in" the corresponding strengths within your answers to the questions. For instance, in the above example, about the angry family member, you could stress your communication skills: "First, I would allow the family member to vent. Next, I would try to determine, specifically, what aspect of patient care he's unhappy with. I would stay calm and empathetic." Etc. It's extremely helpful for both situational and behavioral interviewing to practice with friends.
A phone interview can be somewhat intimidating because you can't see your interviewers' reactions to your responses, and that makes it hard to gauge how you're doing. (I've participated on both sides of phone interviews before.) You should expect to be on speakerphone or a conference call with multiple interviewers. One hour seems like a long time for a phone interview, especially since one would think this is basically a screening interview. So you have my sympathy there!
Couple of tips for a phone interview: don't be afraid to pause to consider your answer, but if you do that be sure to say something like, "I'm taking a moment to gather my thoughts," so they know you're not floundering. Try not to stutter or use fillers like, "Um." Find a comfortable chair to sit in so you are able to BREATHE. (Seriously!) Smile when you answer, because it will come across in your tone. Avoid distractions; for example, put your dog out in case she barks in the middle of your interview, turn off the TV/radio, etc. Have paper and pencil handy and write down the interviewers' names so you don't forget; also, you can jot notes about the questions if you think you will find it helpful.
If you do a Google search on "situational interviewing," you'll find quite a few resources. Good luck to you! Maybe you could let us all know, after the fact, what types of questions they asked you and stuff, in case this is becoming a new trend in healthcare employment.