1) Phone Interview: Really basic. One of the PT managers calls and pretty much gets to know you, ask a bit about your experience and "why Equinox?"
2) One-on-One Interview: Self-explanatory. You meet in person with one of the PT managers. They discuss your experience more in depth and ask things like "Where do you see yourself in 5 years?" and "What's going to be your biggest challenge you face here at Equinox?" Again, they're trying to see if you can handle the industry and if your expectations are realistic in regards to the hours, the pay, the floor shifts, availability, etc.
3) Group Interview: You meet at one of the Chicago locations with all of the other PT candidates (there were about eight of us) and one or two managers from each Chicago location is there too. First, they do a team-building "get to know you" exercise where you have to relate to someone else in the room with two random facts. Then, two managers take turns and perform a really bad squat and a really bad push-up, and you have to chime in and try and correct them. Finally, they split you up into groups of two or three and pair you with a manager to do a case study. You get a client's lifestyle history, medical information, injuries, age, etc and you have to make a two-week program for them and present it to the room. You get 20 minutes.
Basically, they want to see that you're confident, eager to learn and work on any weaknesses, and have the ability/potential to be a good trainer and coach.