Initial phone screening: why you fit (interests, strengths, involvement, etc.), what you know about SpaceX, what you know about the industry, this is where the basic interview questions appear
Technical phone interview:
Part 1: explaining design projects you've worked on (why you did what you did), hands-on experience you have (why you did what you did), machine shop skills and when you have used them
Part 2: fluid dynamics, hydrostatics, statics - not so much if you immediately know the right answer, but, with help, can you arrive at the right answer and display understanding of why