Why is it getting big brown spots
Brown leaf spots on Ficus lyratas are generic symptoms with several possible cause, including improper light and improper watering.
Your Lyrata has to be right in front of a very sunny window that is completely uncovered throughout the daylight hours. If it is more than a couple of feet away from the window or off to the side or in a corner, it is not getting adequate light.
Water your Lyrata as soon as the surface of the soil feels almost dry. Add enough water so that a small amount trickles through the drain holes. If your local tap water is hard, use filtered or distilled water instead.