The Apple MacBook (Early 2015) works well with LG 27UD88-W Monitor over USB Type-C but sometimes you want to make more use of the monitor's great looking screen with other devices. Fortunately, the LG 27 inch Class Ultra HD IPS 4K 27UD88-W Monitor also has one standard DisplayPort 1.2 and two HDMI 2.0 ports supporting 4K@60Hz which you can use to easily connect other devices.
With certain USB Type-C phones like the LG G5, you can actually output DisplayPort directly from the phone to the LG monitor simply by using the Google USB Type-C to DisplayPort Cable. The Google USB Type-C to DisplayPort Cable connects to the DisplayPort connector on the back of the LG 27 inch Class Ultra HD IPS 4K 27UD88-W Monitor and the USB Type-C connector on the bottom of the LG G5.
Just make sure your LG 27 inch Class Ultra HD IPS 4K 27UD88-W Monitor input is set to DisplayPort, and you should be able to see the G5's screen mirrored onto the LG monitor.