VoLTE means Voice over [LTE][1]. The icon notifies you that you are now able to phone over LTE. This means, it's not necessary in order to make a phone call to switch back to 3G (You cannot phone over normal LTE).  
In short it's new and better. As far as I can tell you could disable VoLTE altogether, but I recommend you to simply live with it.


  [1]: https://en.wikipedia.org/wiki/LTE_(telecommunication)