I have read threads where people say that your phone needs a compass to work properly with DJI GO 4 and the Spark; on the other hand, I have read threads where people say your phone doesn't need one.
So, does the mobile device you are using with the Spark and GO need a compass to function fully?

Thanks.

Hi ThatChapSparky, we do appreciate you interest in our products. In my experienced, I calibrate my DJI Spark without any mobile device compass installed in it and everything is perfectly fine. The mobile device will only serve as a monitor for me to follow the instructions on how to properly calibrate the compass. However, I want to be sure about this query. I will forward your concern to our designated team for clarification. Appreciate your patience and support

The mobile device compass only helps you to find in which direction the AC is when you lose visual line of sight. It helps you point the RC in the right direction by using the Attitude indicator even when you cannot visually see the AC. Apart from that there is no limitation of not having a compass on your mobile device. You can get the full functionality of the Spark even without it.

My apologies for the late update. After confirming this concern to our designated team, it is not necessary to have a compass installed on the mobile device/ tablet for your DJI Spark to fully function. Should you need further assistance, please feel free to contact us. Thanks for choosing DJI!

DJI Paladin Posted at 4-25 14:09
My apologies for the late update. After confirming this concern to our designated team, it is not necessary to have a compass installed on the mobile device/ tablet for your DJI Spark to fully function. Should you need further assistance, please feel free to contact us. Thanks for choosing DJI!

Thanks a lot, DJI Paladin.  This was all I needed.

ThatChapSparky Posted at 4-25 22:33
Thanks a lot, DJI Paladin.  This was all I needed.

You're welcome. Enjoy and always fly safely!