Q - What is the belief of phased Raptures?

A - The belief of phased Raptures is:

Phase 1:
There will be a first fruits Rapture that will happen sometime from the start of the Jewish feast of first fruits to the day of Pentecost. This year (2009) that would be April 11, till May 31.

This first fruits Rapture is a special blessing for the "True Christian" you have to be keeping the commands and word of God, you have to have a close personal relationship with him to be found worthy and to be taken in this Rapture, lukewarm and backslidden Christians will not be taken in this Rapture.

Phase 2:
1260 days (about three and one half years) later there will be a second chance Rapture for those left behind and for new believers, this will happen just before the start of the 'great tribulation' this is the second 1260 of the tribulation this is when God will truly send his wrath on this world and most that are left after that will die.

Phase 3:
At the end of the tribulation the good and bad people will be separated into two groups (the Bible calls them the sheep and goats) and the good will be saved and go into the new 1000 year kingdom of Christ to live out their lives and to repopulate the earth. The bad will be cast into the lake of fire forever.

I will say there seems to be good reason to think there will be a second rapture around three and a half years after the first fruits rapture, this one would be for new believers in Christ and for those Christians that were not "overcomers" at that first rapture, if those Christians left behind at the first rapture have become "overcomers" and did not take the mark of the beast or did not worship the antichrist then they will be taken at this second rapture before the start Great Tribulation (this is the second half of the tribulation).

Why do I believe there may well be a second rapture?

Revelation 7:9
After this I beheld, and, lo, a great multitude, which no man could number, of all nations, and kindreds, and people, and tongues, stood before the throne, and before the Lamb, clothed with white robes, and palms in their hands;

This great multitude that just now comes into heaven are not the Christians that were taken in the first rapture because the group from the first rapture are there already in heaven when this group comes into heaven.

Revelation 7:13-14
And one of the elders answered, saying unto me, What are these which are arrayed in white robes? and whence came they? And I said unto him, Sir, thou knowest. And he said to me, These are they which came out of great tribulation, and have washed their robes, and made them white in the blood of the Lamb

The Elders are the people taken in the first rapture, so those arrayed in white robes must be the people taken in the second rapture.

For more information on why there will be two Raptures see my article on (Phased Raptures)