Accurate measurement of hydrophone phase response is critical for underwater acoustic detection， communication， and metrology. However， in open water environments， multipath reflections and ambient noise often cause traditional methods to fail. To address this issue， a high-robustness phase detection method based on the time delay spectrometry （TDS） technique is proposed. By transmitting a broadband linear frequency modulated （LFM） signal， it leverages the linear time-frequency coupling characteristics of the chirp to establish a time delay-frequency domain correlation model. Combined with a controllable time window to effectively isolate the direct sound from boundary reflections， this approach significantly suppresses multipath interference. In laboratory tests within an anechoic tank， phase difference measurements across three different hydrophones showed errors <±1.3°. To validate field applicability， real-world testing was conducted in Qiandao Lake. Using TDS method successfully overcame challenges from surface waves， suspended particle scattering， and lakebed reflections， extracting phase deviations <±2° across the entire measured frequency band， confirming its anti-interference capability. Further analysis demonstrates that TDS effectively suppresses environmental noise through time-domain gating （10 ms window width） and achieves phase decoupling without relying on prior sound speed models.