Not a real Ps user either, but it sounds like you're looking
to display the image in Ps with pixel aspect ratio correction.
Adjust pixel aspect ratio
"To help you create images for video, Photoshop has
a Pixel Aspect Ratio Correction viewing mode that
displays images at the specified aspect ratio."
This Pixel Aspect Ratio Correction in Photoshop is only for viewing.
If you want the correct PAR for stills you need to do that in PS.
Set up a 1920x1080 or 1280x720 canvas with square pixels in PS
Put your still into this canvas and stretch to fill.
If you are only going back and forth in Premiere and PS the PAR gets corrected (for view only).
Only if Pixel Aspect Ratio correction is on in PS. Premiere does in automatically.