ClearUserLog();
//Log Time Started
UserLog("Script Started at" + gs.nowDateTime());

//Query Table
var gr = new GlideRecord('sys_user');
gr.addNotNullQuery('mobile_phone');
gr.query();

//Update Records
while (gr.next()) {
    gr.mobile_phone = "";
    gr.setWorkflow(false);
    gr.update();
}

//Log Time Ended
UserLog("Script Ended at" + gs.nowDateTime());