To solve this problem, we need to identify the phase during which DNA replication occurs in eukaryotic cells.$\newline$Eukaryotic cells undergo a cell cycle consisting of several phases:$\newline \bullet$G$_1$ phase (Gap 1): This is the first phase after cell division where the cell grows and carries out normal functions.$\newline \bullet$S phase (Synthesis): During this phase, DNA replication occurs. The cell synthesizes a complete copy of the DNA in its nucleus.$\newline \bullet$G$_2$ phase (Gap 2): This phase follows DNA synthesis and is a period of further growth and preparation for mitosis.$\newline \bullet$M phase (Mitosis): This is the phase where the cell divides its copied DNA and cytoplasm to form two new cells.$\newline$Given this information, DNA replication specifically occurs during the S phase of the cell cycle.$\newline$Therefore, the correct answer is Option 2: S phase.