Detail info: http://www.ieee.org/web/membership/senior-members/guide.html
Highlight: In particular, your resume should highlight those areas of your experience that go towards meeting the requirement for 5 years of Significant Performance.
A PhD study will be counted for certain years, I don't remember how many. You need 2 to 3 senior member’s recommendation letters. That should not be very hard for you. IEEE grants senior members twice a year when the IEEE board holds a meeting.