Freeze an Atomic at a precise distance below the door in order to crouch-jump up and clip through the door shell. Freezing it while it is moving horizontally and Samus is standing works as a trivial setup. If Phantoon is not defeated, stand on the stairs so that Samus is just a few pixels lower, then freeze the Covern low in its cycle. Alternatively, freeze it high then perform a tight down grab to get onto it for a pixel perfect clip.