Phleomycin is primarily used in molecular biology and genetic research as a selective agent. It is effective in selecting transformed cells that carry resistance genes, particularly in bacteria, yeast, and plant cells. In plant biotechnology, it is employed to screen for genetically modified plants that have incorporated the phleomycin resistance gene, ensuring only the desired transgenic plants survive. Additionally, phleomycin is utilized in studies involving DNA damage and repair mechanisms due to its ability to cause double-strand breaks in DNA, making it a valuable tool for investigating cellular responses to genetic damage.