Where in the cell cycle is the cell's DNA actually copied?

During Mitosis, DNA is replicated during the S phase (Synthesis phase) of Interphase. Interphase is basically the daily life cycle of the cell. Cells spend most of their life in Interphase before Mitosis occurs (M phase).

Interphase is the longest part of the cell cycle. This is when the cell grows and copies its DNA before moving into mitosis. During mitosis, chromosomes will align, separate, and move into new daughter cells. The prefix inter - means between, so interphase takes place between one mitotic (M) phase and the next.