Hello 
cannot assign one task to multiple people on iPhone app. Or am I missing something? When tapping on assignee, there is no option to tap on “assign to multiple”. 
Please help
The Asana policy is one task = one assignee. You could duplicate the task or assign multiple subtasks.
Hello @Karien_van_der_Westh - At the moment this functionality is not available in the mobile app. I will happily submit this to our team for you as a product feedback suggestion!