Is this the right way to write 'add contact' view

Question

I'm using DRF. I have a User model and contacts field in it and contacts are also User instances.

class User(AbstractBaseUser, PermissionsMixin):
    first_name = models.CharField(
        _("first name"),
        max_length=30,
        blank=True,
    )
    last_name = models.CharField(
        _("last name"),
        max_length=150,
        blank=True,
    )
    phone_number = PhoneNumberField(
        unique=True,
        blank=False,
        null=True
    )
    contacts = models.ManyToManyField("User", blank=True)

This is the serializer.

class AddContactSerializer(serializers.Serializer):
    phone_number = serializers.CharField(max_length=12, write_only=True, required=True)

    def update(self, instance, validated_data):
        user = self.context['request'].user
        phone_number = validated_data["phone_number"]
        added_contact = User.objects.get(phone_number=phone_number)
        user.contacts.add(added_contact)
        return UserSerializer(added_contact)

And the view.

class AddContact(APIView):
    permission_classes = [IsAuthenticated]

    def post(self, request):
        serializer = AddContactSerializer(
            request.user, data=request.data, context={"request": request})
        if serializer.is_valid():
            serializer.save()
            return Response(data=serializer.data, status=status.HTTP_201_CREATED)
        return Response(serializer.errors)

I'll need to add error handling though.

Thank you for reviewing this.