Are you in a Discord call at the same time? On some computers Discord will take priority control of the mic, which can cause issues in some (not all) games. Some friends and I will deafen in Discord whenever we played some games with proximity chat, and I had that issue in a few games.
If you're not in a Discord call, try verifying your game files. It's possible Steam missed something when you downloaded the game, and verifying it will have it check to see if any files are missing or corrupt, and replace/repair them if so.
https://help.steampowered.com/en/faqs/view/0C48-FCBD-DA71-93EB
Something I've also had work in other games, which I'm sure you probably already tried but thought I'd mention it anyway, is restarting your computer. I tried playing Phas once after another game that had proximity chat -- can't remember what it was called, been a while -- and restarting was the fix to get it working for me.
If the above doesn't work, can you let me know which mic you're using, and if you're using an audio mixer/interface along with it? Such as a GoXLR