The phrase is "A city upon a hill."
This phrase became the name for one of Winthrop's most famous speeches. Before arriving in the Massachusetts Bay Colony, Winthrop gave a speech to his fellow Puritans about the importance of unity, working together, and creating an ideal society in which people followed God's teaching. Winthrop's goal was to develop this utopian society in order to be a model for other European settlers coming to the New World during the 1600's.
The idea of a "city upon a hill" was used in the Bible (Matthew 5:14), hence explaining where Winthrop got the idea from.