The DNA is condensed into visible chromosomes in the first phase of mitosis, known as prophase.
The cell cycle. Actively dividing eukaryote cells pass through a series of stages known collectively as the cell cycle: two gap phases (G1 and G2); an S (for synthesis) phase, in which the genetic material is duplicated; and an M phase, in which mitosis partitions the genetic material and the cell divides. 1  G1 phase. Chromosomes replicated during the S phase are divided in such a way as to ensure that each daughter cell receives a copy of every chromosome. In actively dividing animal cells, the whole process takes about one hour. Interphase begins with G 1 (G stands for gap) phase. During this phase, the cell makes a variety of proteins that are needed for DNA replication. S phase. During S phase, which follows G 1 phase, all of the chromosomes are replicated. Following replication, each chromosome now consists of two sister chromatids (see figure below). Each chromosome contains a single double-stranded piece of DNA along with the aforementioned packaging proteins. Figure 1: Chromatin condensation changes during the cell cycle. During interphase (1), chromatin is in its least condensed state and appears loosely distributed throughout the nucleus. Chromatin condensation begins during prophase (2) and chromosomes become visible. Mitosis. Mitosis is a form of eukaryotic cell division that produces two daughter cells with the same genetic component as the parent cell. Chromosomes replicated during the S phase are divided in such a way as to ensure that each daughter cell receives a copy of every chromosome. In actively dividing animal cells, the whole process takes about one hour. Confidence votes 36. DNA condenses before a cell divides in two, in order to produce more cells (more specifically in the mitosis phase of the cell cycle). DNA condenses into typical structures called chromosomes, that can be seen in electron microscopes Close. Chromatin condensation changes during the cell cycle. During interphase (1), chromatin is in its least condensed state and appears loosely distributed throughout the nucleus. Chromatin condensation begins during prophase (2) and chromosomes become visible. Chromosomes remain condensed throughout the various stages of mitosis (2-5). 1  Add Content to Group.  The DNA is condensed into visible chromosomes in the first phase of mitosis, known as prophase. All cells, whether plant or animal, undergo mitosis in order to make new cells.  Figure 2: A the appearance of DNA during interphase versus mitosis. During interphase, the cell's DNA is not condensed and is loosely distributed. A stain for heterochromatin (which indicates the position of chromosomes) shows this broad distribution of chromatin in a mouse cell (upper left). The same stain also shows the organized, aligned structure of the chromosomes during mitosis. During interphase (1), chromatin is in its least condensed state and appears loosely distributed throughout the nucleus. Chromatin condensation begins during prophase (2) and chromosomes become visible. In cells with a nucleus, as in eukaryotes, the cell cycle can be divided into three periods: interphase, the mitotic (M) phase, and cytokinesis. During interphase, the cell grows, accumulating nutrients needed for mitosis, preparing it for cell division and duplicating its DNA. 
http://www2.le.ac.uk/departments/genetics/vgec/schoolscolleges/topics/cellcycle-mitosis-meiosis http://cyberbridge.mcb.harvard.edu/mitosis_4.html http://www.nature.com/scitable/topicpage/chromosomes-14121320 http://www2.le.ac.uk/departments/genetics/vgec/schoolscolleges/topics/cellcycle-mitosis-meiosis http://www.answers.com/Q/When_is_the_DNA_condenses http://www.nature.com/scitable/content/chromatin-condensation-changes-during-the-cell-cycle-14710929 http://www.ehow.com/info_12049431_dna-condensed-phases.html http://www.nature.com/scitable/topicpage/chromosomes-14121320 https://en.wikipedia.org/wiki/Cell_cycle
dna condenses during what phase