That is a mouthful, Phase 2 Heightened Alert. Due to a surge in a variant of coronavirus B.1.617.2 variant.
This variant imported from India is especially virulent and spreads very easily. There was a cluster that was created by dining in at Changi Airport. That spread from a cleaner to several other unrelated staff.
So after about 5 months of freedom, we are back to tighter restrictions. 2 visitors and groups of 2 only.