The Indian economy is entering a “productive growth phase” and real GDP growth is likely to rise to 7.9 per cent by December driven by favourable external demand, improving corporate balance sheets and private capex recovery, says a report.A productive growth phase is characterised as a period of improving growth, while macro stability remains in check and typically sets the stage for a sustained growth cycle.According to the research note by Morgan Stanley, growth is likely to inflect higher, accelerating by almost 1 per cent point over the next three quarters.