Cyanobacteria are being increasingly explored due to their ability to directly convert CO₂ to useful biochemicals. Recently, a robust fast-growing strain resistant to abiotic stresses, Synechococcus elongatus PCC 11801 was discovered with growth rate comparable to yeasts. Due to the limited availability of synthetic biology tools, we performed random mutagenesis coupled with amino acid analog selection for the development of Phenylalanine (Phe) overproducers. The best strain produces 1.2 ± 0.1 g Phe l^-1 in 3 days under 3% CO₂. We also report a nutrient feeding strategy that increased the titer to 3 g Phe l^-1 in a 15-day culture. Additionally, selected mutants show no growth reduction compared to wild type but show a 30% increase in carbon fixation.