My iPhone speaker is not working. I can’t hear people talking on calls

Were you able to utilize any portions of the instructions

from Apple Support article which led you to post here?

Certain aspects of this may seem lacking. For example

~ IF there is No Sound from Speaker, no matter what.

And if instructions do not help resolve the symptoms.

Then, you'd need to consider an inspection, diagnostic

&/or service for iPhone; to repair cause of the problem.

[Get Support]

"If you hear no sound -or 'distorted' sound- from your iPhone, iPad..." - Apple Support

Instructions appear helpful enough; I've bookmarked them

into Mac for future reference.. Just in case they're needed.

Also there are some resets for iPhone which may help.

..I've been exploring mine, after battery was replaced;

ended up using Shut Down ~ then, Restart; it helped..