It seems to me a proper reply to him saying something like that would be to respond likewise - via the phone. Texting is for impersonal chat. Before you text, ask yourself, "Would this be better vocalized?" I believe to talk about intitmate or important feelings by text is to trivialize it. You may be giving the message you don't really care. This should be a matter not treated carelessly which is what he may be thinking.

Look, if he feels talking about feelings is important enough to do in a more personalized form you owe it to him to do the same.