An unexpected phone call is a sudden and unanticipated communication from someone over the phone, which is not planned or expected by the recipient. Full definition
The important thing to remember is that however much you try and plan your day out, however much you sit in bed the night before and plan what you will do at 9, 10, 11 o clock, the inevitable unexpected phone call, email or urgent task will quickly disrupt your «perfectly planned» day. (howespercival.com)
Jean - Claude Juncker, president of the European Commission, receives an unexpected phone call during a press conference. (cnbc.com)
An unexpected phone call of such import can really throw you off (frankly, that's part of the agenda), and so I usually recommend that you ask the caller if you can situate yourself in a quiet spot and call back when you have paper and pencil in front of you. (sciencemag.org)