[Answered ]-Django Rest Framework unique field constraint on array

You can customize the behaviour of list of object through list_serializer_class option in meta class. Like this:

class LeadListSerializer(serializers.ListSerializer):
    def validate(self, data):
       items = list(map(lambda x: x['phone_number'], data))
       if len(set(items)) == len(items)):
           return super().validate(data)
       raise ValidationError()
       
class LeadSerializer(serializers.ModelSerializer):
    class Meta:
        model  = Lead
        fields = '__all__'
        list_serializer_class = LeadListSerializer