Your child is now into symbolic play where one object represents another. For instance, he would have seen you talking over the phone. He will replicate the same action by using a banana as a telephone. In this way he is working on his imagination and creativity and using them to understand real life events.
What you need to know
Provide him variety of toys and let him explore. This way he realizes that different toys have different purposes which is important for symbolic play. You can help him work on language while he is busy pretend playing. For instance, if you see him using banana as a phone, you can say, “Let us call grandma and ask, how are you?" If he is using the sofa as a bus, you can sing along rhymes”. Join with your little one and enjoy the fun.