Integer ambiguity resolution (AR) is always desired to achieve ultimate precision in GNSS positioning. Once ambiguities are fixed, initialization time will be remarkably shortened, along with precision improvement. AR is mostly studied on “clean” double- differenced (DD) observations which are generally free from unknown errors and biases. However, it is not true for GLONASS. GLONASS adopts FDMA (Frequency Division Multiple Access) signal system, i.e., satellites transmit signals on different channels. As a result, inter-frequency phase biases (IFCBs) are observed among heterogeneous, even homogeneous, receivers for GLONASS, which severely inhibit DD-AR. IFCBs are presumed to be the same between adjacent frequency channels and, thus, usually are quantified as a linear function of channel number. Although IFCBs model is effective for GLONASS ambiguity fixing and has already been prevalently recognized by GNSS community, it’s not theoretically rigorous and is potentially problematic if carrier-phase hardware biases differ by up to several millimeters across frequency channels. Actually, IFCBs are in essence the outcome of differential code-phase biases (DCPBs), which have been introduced into RINEX (Receiver Independent Exchange Format) 3.03 with header label “GLONASS COD/PHS/BIS”. DCPBs are defined with respect to receivers as biases between pseudorange and carrier-phase measurements, which can be divided into the DSP (digital signal processing) derived and the hardware derived parts. We can effectively determine DCPBs, in the precision of sub-ns, by resolving ionosphere-free ambiguities of ~5.3cm wavelengths. In this study, we estimated 7 years (2012-2017) of DCPBs products per station with median and long baselines in IGS network. Our DCPBs products display 1-2 ns daily variation for most of stations. With our estimated DCPBs products, GLONASS double-differenced ambiguity fixing rate can reach beyond 96% between heterogeneous receivers distanced by even 1500 km. We storedthose GLONASS phase bias products in the bias-SINEX format, in addition to GPS FCB (Fractional Cycle Bias) products, and can be freely accessed from the FTP of Wuhan University IGS analysis center.