Is the first resurrection mentioned in Revelation 20:4-6 a physical bodily resurrection or spiritual?
When we read of the "first resurrection" it is ALWAYS the bodily resurrection of Christ! Because it is through His resurrection life that mankind MUST have part in to overcome the second death, and in fact the only way to both know and enter the (spiritual) Kingdom of God!
Christ is not only the "FIRST RESURRECTION" from the physically dead to immortal life, but His spirit is also the first to return to the Father after His body died.
Luke 23:46 (KJV) And when Jesus had cried with a loud voice, he said, Father, into thy hands I commend my spirit: and having said thus, he gave up the ghost.
Ecclesiastes 12:7 (KJV) Then shall the dust return to the earth as it was: and the spirit shall return unto God who gave it.
This is how the gates of heaven are now opened for all who have part in the "first resurrection" through the life and death of Christ. By making atonement for sin, and defeating death, Christ made the way to heaven open. That's why before ascending to heaven Christ first descended into the place of the dead to set free those who before His coming had been spiritually held in bondage to the grave. Christ took them with Him through His Spirit, and having access to heaven they are now the spiritual body of believers there.
Ephesians 4:8-10 (KJV) Wherefore he saith, When he ascended up on high, he led captivity captive, and gave gifts unto men. (Now that he ascended, what is it but that he also descended first into the lower parts of the earth? He that descended is the same also that ascended up far above all heavens, that he might fill all things.)
The problem premillennialists have is an inability to understand things they cannot see! You're preoccupied with flesh and seem to think that unless man is bodily resurrected after death, they have not had part in the "first resurrection" that is not physical but spiritual.