What's the difference between phone interview and an in person interview?

I'm applying for an accounting position and they require that I go in for an interview. But I've also heard that some only require a phone interview? Why do some require an in person interview and some only require a phone interview?

Thank you!

Usually accounting postions always require an in person interview. The management has frequent contact with their accountants and they want to be sure the prospective employee is the right fit for the job. Phone interviews are usually for short term consultant/contractor positions.

They are the same--except phone interviews you can do in your pajamas