Apple Activity March Challenge can anyone explain calculation?
Your phone’s math looks off. I’d contact support in case they have a unit error in your locale. In the US I can confirm from three different people, we have pretty aggressive goals set. One person is far less active than me and far less calories on their goal. Another works out a lot more and has a much higher increase needed in their daily burn. 

My goal was 25,015 calories and I’m barely going to make it tomorrow on the 29th having worked out at least once a day which is far more than I did all year.