This study investigates the sensitivity of the phase observations of Global navigation satellite system Reflectometry in order to monitor coastal water level fluctuations. At low satellite elevation angles, the reflected signals cover wider area but utilizing them would be more complicated. In this paper the utilized Global Positioning System observations are collected at very low elevation angle “called grazing angle” through the year 2014 and analyzed by phase and phase rate retrievals. The phase retrieval results for PRN 25 show the residual height precision and offset of about 25 cm and 10 cm at the elevation angles of 5° to 8°. In the case of PRN 10, the precision and the offset of the residual height are estimated about 35 cm and 10 cm at the elevation angle of 4° to 8°.