You could try email, often Mark answers emails even when he isn't in the office. I would guess they would be back after the first. It's also a very small operation, so it might just be that no one was free to pick up the phone. Did you leave a message?
Mark isn''t coming back until next week so you may have to wait. He also doesn''t seem to be responding to emails (at least not to mine) but I can wait.