What are the three phases of interphase? what happens in each phase?

The stages of interphase are:
G1 (Gap 1), in which the cell grows and functions normally. During this time, a lot of protein synthesis occurs and the cell grows (to about double its original size) - more organelles are produced and increasing the volume of the cytoplasm. 
Synthesis (S), in which the cell duplicates its DNA (via semi-conservative replication). During S phase, the centrosome is also duplicated.
G2 (Gap 2), in which the cell resumes its growth in preparation for mitosis.

I hope this helps!