It is always the best practice to have a fix public IP address where you are hosting your 3CX server. Especially if you are going to have remote ext. But if that is not an option. Checking in with your public ip and change it manually as need is possible. If you dont mind doing all the work when your IP change. Anyways, after looking at your screen shoots again. I've notice you have setup your softphone wrong. By default, the sip proxy manager listen to clients (in this case, your softphone and your cisco phone) on port number 5080. In your screen shoots, one was set to 5090 and the other was set to 5060 which are incorrect. And that should be the reason why you have no audio. with the 3cx softphone and the cisco spa50X phones, you can totally bypass the proxy and register your phone with the public IP address where your 3CX server is. However, you will need to changes the IP address everything your ISP assign you a new one. If this is just for fun or a testing project, this setup is fine. But if it is in a production environment, I strongly suggest you to get a FIX public IP from your ISP.