/usr/share/php/Symfony/Component/Serializer/Encoder/ is in php-symfony-serializer 2.7.10-0ubuntu2.
This file is owned by root:root, with mode 0o755.
..
/usr/share/php/Symfony/Component/Serializer/Encoder/ChainDecoder.php
/usr/share/php/Symfony/Component/Serializer/Encoder/ChainEncoder.php
/usr/share/php/Symfony/Component/Serializer/Encoder/DecoderInterface.php
/usr/share/php/Symfony/Component/Serializer/Encoder/EncoderInterface.php
/usr/share/php/Symfony/Component/Serializer/Encoder/JsonDecode.php
/usr/share/php/Symfony/Component/Serializer/Encoder/JsonEncode.php
/usr/share/php/Symfony/Component/Serializer/Encoder/JsonEncoder.php
/usr/share/php/Symfony/Component/Serializer/Encoder/NormalizationAwareInterface.php
/usr/share/php/Symfony/Component/Serializer/Encoder/SerializerAwareEncoder.php
/usr/share/php/Symfony/Component/Serializer/Encoder/XmlEncoder.php