"Torn Asunder" by John Ostrander and Tom Mandrake.
As you can see from the cover, the Martian Manhunter fights Etrigan, the Demon, which means there's a good chance The Phantom Stranger will be hanging around.
After The Sentinels of Magic (Sentinel, Ragman, Blue Devil, Zatanna, etc.) try and subdue him, The Phantom Stranger makes an appeal to J'Onn:
After this, though, the Stranger is nowhere to be seen. Surely he had "More pressing matters to attend to."