Calculating phase voltages from line voltages in an unbalanced 3-phase system can be achieved using voltage-phase vectors, especially when the nature of the imbalance is known. Understanding the specific imbalance is crucial, as it affects the calculations. Adding new loads can further shift the existing imbalance, complicating the analysis. Accurate calculations require careful consideration of all loads in the system. Properly addressing these factors ensures more reliable phase voltage determinations.