you can try a couple of things . i use webex all the time and i make sure the media volume is cranked up 100% and notice the speakerphone is louder. second try and turn off Bixby Voice i had to to do that to turn off echo issues with webex and teams while using speakerphone.
You should be able to google how to turn off Bixby Voice and get a bunch of posts.
hope that helps!
If the device is working with the stock app, I would recommend reaching out to the developer of the app you are experiencing these symptoms with for further assistance.
Do you experience these symptoms with the stock phone app on your device?