This is PHP container with Composer installed, and the dependencies it needs (patch, git).
This is part of the Exove's Local-docker stack for PHP development (namely Drupal projects).
However, this can be used individually as well:
$ docker run xoxoxo/php-composer:7.3-1.3 bash -c 'php -v; composer --version'
PHP 7.3.27 (cli) (built: Mar 6 2021 05:59:52) ( NTS )
Copyright (c) 1997-2018 The PHP Group
Zend Engine v3.3.27, Copyright (c) 1998-2018 Zend Technologies
with Zend OPcache v7.3.27, Copyright (c) 1999-2018, by Zend Technologies
with Xdebug v3.0.3, Copyright (c) 2002-2021, by Derick Rethans
Composer version 2.0.11 2021-02-24 14:57:23
See https://github.com/Exove/php-container/tree/7.3/
There are versions with PHP 7.1 , PHP 7.2 and PHP 7.4.