Many newer phones have screen mirror software preinstalled. Open the shortcuts menu by dragging down from the top of the screen, you should see different thumbnails such as Bluetooth or torch. You are looking for the screen mirror/projector. If it isn't showing click the pencil icon at the top to edit and see if it is in the list that appears. If you have it click it and your TV should appear in the pair option. If it doesn't you will have to go into the TV settings and select the stream from external device option, source /connection guide /mobile device /screen sharing (smart view).
If your phone does not have the option download allcast or something similar.