Complex sentence: She was the consort to King Eric of Pomerania, the de facto regent of Sweden in 1420 and the regent of Denmark and Norway from 1423 to 1425.
Split into simpler sentences: She was the consort to Eric of Pomerania, who ruled the three kingdoms. Queen Philippa served as the de facto regent of Sweden in 1420 and the regent of Denmark and Norway from 1423 to 1425.