This sort of area has all sorts of odd versions of fonts floating around, and it may be that you have a conversion of a conversion that has incorrect flags set, implying the font is regular when it’s bold and or vice versa. When I get stuff like this, I pray fervently that the original text and font is properly Unicode-compliant and ask my client if I can switch to a “cleaner” font.
In this case something like the Noto Sans family from Google comes to mind. https://www.google.com/get/noto/
It’s public-domain and generally trouble-free.
I checked out Phetsareth OT on a search and found a source here: https://www.phetsarath.gov.la/download.php (top of list). That appears to be Regular in weight to me.
ALTERNATIVELY – I wonder if you have a case of someone setting the text with an outline around it in order to create a pseudo bold look? That would be curable by a simple search and replace.