If you stay in the first person POV (and not shifting POVs is the preferred approach for short stories) then you need to find a way to get the character in the scene. It could be through a recording, allowing them to participate after the fact reacting to what was said in the scene. It could be a listening device -- like an open phone line -- and the narrator can react in real time to what is said.
If the only solution that works for your story is shifting the POV, you can move to another character, but you risk sublimating or diluting your engagement with your main character.
Or you can move to an omniscient POV. Be clear that your MC is somewhere else, doing something else as part of establishing the scene sans MC. The upside of omniscient POV is the expectations of engagement are lower. But, it also means you are more dependent on dialogue and actions to convey character motivations and intent.
To avoid that jarring sense that other writers complain about when you are shifting POV, establish early in the story that omniscient narration is part of the story. If you hook is in an omniscient POV, then drifts into the 1st person POV for most of the story, then the readers won't be surprised when the narration drifts out of the 1st person POV to an omniscient POV.
This technique is used mostly in 3rd person POV -- read S King or S Collins for examples -- but there isn't any reason it can't be used for 1st person POV, other than it is more challenging to pull off successfully.
I think if your story drifts between 1st person POV and omniscient narrator repeatedly, like when the character reacts to an event in the story, and then the narration drifts out of 1st to omniscient POV to share backstory or put the event in context before falling back into 1st POV then it will be seen as part of the voice of the piece.