The “just sit and wait for the Phony War to end in April 1940” option is a bit perplexing as an answer to “You are the German High Command! What is your next Combat Movement?” because it seems to imply that the Phony War was operating on a fixed timetable, and that this timetable was in someone else’s hands. The lack of action on land on the Western Front is certainly due in part to inaction by France and Britain (whose strategy was basically to sit around for a couple of years to built up their strength for a showdown, while simultaneously hoping that the Nazi regime would be overthrown by a coup), but it was also very much a deliberate choice by Germany. The Wehrmacht needed to analyze the Polish Campaign, fix the tactical and operational elements that hadn’t worked as well as expected, plan the upcoming campaign against France and the Low Countries, rest and replenish its forces, give them more training, provide them with additional equipment, and redeploy them to the west. Doing this properly took time, but Germany could afford to take the time to do the job right because of the lack of Anglo-French pressure on the western front. ( In other words, by sitting on their collective hindquarters France and Britain surrendered the strategic initiative to Germany, which gave the Wehrmacht the luxury of attacking at the time and place of its own choosing.) Moreover, the time period during which these activities took place were the fall of 1939 and the winter of 1939-1940, which was conveniently timed because this meant that the Wehrmacht wouldn’t have to fight in the fall (manageable, but rainy and muddy) or in the winter (far less harsh in the West than in Russia, but still potentially nasty as veterans of the Battle of the Bulge will recall). The late spring / early summer period chosen for the offensive in the West was much more congenial for military operations.
