Can any one tell me what is the phase angle and what is the concept behind it?
Have you tried google?
Phase describes how are particles oscillating.
Lets simplify this with a particular case in which a particle is describing SHM about a horizontal line. It will oscillate with certain amplitude (say A) . At any instant it will have displaced certain distance from its mean position (say x; -A ≤ x ≤ A) . Now consider a circle of radius 'A' units. The angle that the radius vector of the circle makes with horizontal axis such that the projection of the radius vector on the horizontal axis is equal to the horizontal displacement of particle is called the phase angle (of the particle at that instant of time).
So if phase angle is 0 at any instant then it says particle is at extreme position at that instant
If phase angle is quarter of ∏ ie 45° it says particle is at x= A/√2.
So phase angle describes where is the particle and how is it moving at any instant.
Hope you got something out of it.
Separate names with a comma.