phoenix, I think it's fine to call to talk to him for a minute or two to see if he is OK. You care about him and just stopped seeing him recently. It is perfectly normal to be concerned for his health, especially since he made not secret of it to you that he was having surgery. I wouldn't worry about interrupting him in session. Most likely, he turns off his phone while in session and you can leave him a voicemail and ask him to call back. I don't vote for sending him a card, because that is one way. It only tells him you care about him and doesn't reassure you that he is doing OK. So I think a call is best for what you want to know.