This research looks at a partial replacement of asphalt-rubber (AR) binder by Guayule Resin (BGR), at least to compensate the original asphalt (AC) high-temperature performance. In particular, storage stability and phase separation (essential parameters affected by modified-binder storage) were addressed in this regard. AR-BGRs were compared to their corresponding ARs, to judge the BGR contribution. The binder whole matrix (WM) storage stability relied on the viscosity, density, and CRM dissolution. Measurements related to these parameters and storage stability were taken. Thermogravimetric analysis (TGA) was used to analyze CRM dissolution. Comparisons between WMs vs. liquid phases (LPs) were established as could show the variation between their storage stability and LP separation. Rheological analysis by master curves was provided for top and bottom fractions of WMs and LPs to judge the effect of remaining CRM (residue) and LP separation on the behavior. TGA and Fourier-transform infrared spectroscopy (FTIR) were utilized to verify the LP separation analysis. Outcomes showed that AR-BGR WMs yielded lower storage stability compared to ARs. The authors see that the viscosity difference between AC and BGR was the crucial reason. Nevertheless, perfect storage stability and no LP separation were observed with either AR-BGRs or ARs as proven by rheological analysis and verified by TGA and FTIR analyses for selected binder fractions. Accordingly, the study claimed BGR (PG52) could replace a portion of AR on the LP scale to at least compensate the original asphalt (PG64) performance (e.g., LP of 75%AR (including 20%CRM by wt. of AC) plus 25%BGR).