I had the same issue and called customer service.
They told me to change the following setting.
Tap on Connections
Open Mobile Networks
Tap on Network mode
Change this setting from LTE/3G/2G to 3G/2G. You cannot make this change while on a call.
For some reason, this setting is actually 4G/3G/2G, but the S9 doesn't say that.
When you make a call, it will still show HD call, but not HD plus like with the LTE setting.
This has helped me a lot with the muffled speakerphone issue.
Hope it helps you.
Thanks so much. I'll try that
Thank you! I got my S9 a couple days ago and so did my husband and man I was going crazy with the call quality and speaker quality. I changed the settings and it is way better!
I know this is a fairly old thread but to be honest I find it appalling that the suggested solution is to turn off one of the major reasons for purchasing this phone (LTE). This is NOT a solution but just an avoidance of the problem.
I recently purchased an S9 and am finding it to be probably the worst phone I have ever owned. Hardly a day has gone by when I have not had some issue that I have spent hours trying to resolve. Some I have just thrown my hands up and given up on.
The speakerphone absolutely stinks and is basically unusable unless I put my mouth right up to the microphone, thus pretty much defeating the purpose of a speakerphone to begin with.