Why were the early months of works war 2 referred to as the phony war?

The early months of World War II, from September 1939 to April 1940, were termed the "Phony War" because, despite the formal declaration of war between the Allies and Germany, there was a notable lack of significant military operations on the Western Front. After the rapid invasion of Poland by Germany, both sides engaged in limited troop movements and preparations, but no major battles occurred, leading to a sense of inactivity and anticipation. This period ended with Germany's invasion of Denmark and Norway in April 1940, which marked the beginning of more intense military action.