Groundhog Day for Phil

I'm a baby groundhog living underground in a den. Snow is above me. Living in a cold place, I grow two coats of hair. One is gray-white and the other layer is thick brownish. I'm grown up now. My name is Phil because I like to "fill" myself up with food such as clover plants. Everybody is excited about today. It is February 2nd. Why are they gathered around my burrow.