My indoor rubber tree is losing its leaves and those that remain are very small.
My Indoor Rubber Tree Is Losing Leaves
If this plant was bigger when you got it, and it's gradually been losing its big leaves, and the ones it grows have been getting smaller, in all probablility you've been keeping it too wet. Many varieties of Ficus, rubber tree among them, are super adaptable plants, and they can adjust to rather low light, but only if the soil is allowed to dry almost completely between watering. That means you must check the soil all the way to the bottom of the pot. This video will tell you a little more about soil testing http://www.youtube.com/watch?v=Tf-8InSamYQ
Also, try to move it to a spot with more light. While rubber trees can adapt to lower light, they are not low-light plants. Moderate light - general working light for an office, or near a north or east window - is at their lower level of adaptability.
Hopefully, this article will help: https://www.gardeningknowhow.com/houseplants/rubber-tree/how-to-care-for-a-rubber-tree-plant.htm
Since these trees grow in full sun in their natural habitat, I've found it difficult to give them too much sun. It seems the problem is acclimating it to lower light when moved inside for cold weather. Also, as the plant ages and the stems grow, the older leaves shed. This is common on dracaena, ficus, scheffelera, arboricola and agleonema. Small leaves are usually an indication of insufficient nutrition and/or light.