Interesting that page 44 of the P3A manual instructs you to not carry ferromagnetic materials with you during calibration such as keys or cellular phones. But the calibration is initiated from an app running in a cell phone.
Initiated, not completed. Initiate, walk away from the bird, put controller on ground, walk back to bird, do the dance, go get the controller, take off.
PS, its a DJI c.y.a. thing. I've never not had my cell in my pocket when calibrating my V+. Nice thing about compass problems is you know immediately in the initial hover whether something is wacky.