My husband is a very shy guy and we hardly talk at home. However, her has a lot to talk to on the phone with his parents and other friends. What could be the reason for his aloofness?

Give him sometime to open up. And if it is his nature then you can hardly do anything. To make your bond stronger, you can strike conversation with him. As you mentioned, he talks a lot with his mom and all, that means that he is not a quiet person and like to talk. So, if he doesn't initiate conversations, you can. Pick up the topics which he has interest in, or try to be part of his hobbies. Figure out if you both have common interests and if yes, then bonding with him would be easy. Figure out, what are his expectations from you. Try to make out time for yourselves, and things will get hopefully get better.