You don't say which user name you are using for the iPhone user when connecting to the Mumble server.
It should be a different username than what you are using on the RigPi's Mumble client.
It can be any name, so long as it is different. The password will be the same for all users on any given Mumble server.
Also, the recording shows that receive audio is present so the selected device seems to be correct.
Was that recorded on the RigPi from the AlsaMixer input using USBaudioCODEC?
Your images are too blurry for me to read but suggest that you have chosen the USBaudioCODEC for the input and output device on the RigPi Mumble client.
Please cut and paste that text entry into your next message.
This Groups.io shrinks image attachments to the point that they are nearly useless.
73 - Mark - K8MHW
'A RigPi Enthusiast!' - I am not otherwise affiliated with MFJ or RigPi