There is a strong need to develop rapid diagnostic assays for UTIs to identify specific pathogens within hours rather than days. The availability of testing results early can improve patient outcomes, reduce the number of laboratory tests, and reduce intrusive procedures and the length of hospital stays. Current urinary tract infection (UTI) diagnostic methods are slow or provide limited information, resulting in prescribing antibiotic therapy before bacterial pathogen identification. Here, we adapted a gold nanoparticle colorimetric approach that combines the signal amplification of a DNA-based multicomponent nucleic acid enzyme (Mz) with gold nanoparticles (GNPs) for the detection of UTI pathogens. In addition, we developed a smartphone platform for UTI detection, a smartphone device capable of automating the analysis of the colorimetric signal from the GNP-Mz assay. The smartphone will be a critical feature for the automation of the assay and will allow electronic storage of the test data and long-term geospatial tracking of infections. We show the parallel identification of five major UTI pathogens at clinically relevant concentrations of 105 bacteria/mL using bacteria-specific and universal probes. We validated the diagnostic technology using 115 positive and 19 negative samples from patients with Escherichia coli, Proteus mirabilis, and Klebsiella pneumoniae infections. The assay successfully identified the infecting pathogen (specificity: >98% and sensitivity: 51-73%) in 3 h. Our platform is faster than culturing and can wirelessly store and transmit results at the cost of $0.38 per assay.