The icon “4G” tells that the phone is currently connected to a 4G network. If you start browsing and hence downloading/uploading data, the transfer is done over the 4G network. However (since you disabled “4G calling” (VoLTE)), the phone will switch to a 3G or 2G network for phone calls. The icon will show 2G or 3G during phone calls.
“4G calling (beta)” means that the phone supports VoLTE but the implementation is not final. Issues may occur on some networks or use cases.