I guess he's been getting a lot of calls from media organizations, maybe also friends just calling to see how he's doing and if there's been any news.
At first he seemed to just laugh it off as ironic that the phone was ringing (yet again?) right when he was trying to speak to media. I am surprised he didn't jump to check who was calling before having that reaction, just in case it was police calling with news that was more important than the interview.... but I guess he just figured it would be yet another media call that could be put off?
And then when he did take the phone out of his pocket, I think he glanced at it to see who the caller was before shutting the call off, so I guess his assumption was correct that it was something that could wait five minutes.