vagrant upコマンド実行時のエラー

インフラの学習を目的として、ISUCONの過去問をやってみようと思い、このvagrantファイルを用いて環境構築を試みたのですが以下のようなエラーが表示され、うまく環境を作ることができません。
vagrant upコマンドはisucon5-qualifier-standaloneディレクトリ内で実行しました。

==> default: TASK: [command /home/isucon/.xbuild/php-install 5.6.13 /home/isucon/.local/php -- --with-pear --with-openssl] ***
==> default: failed: [localhost] => {"changed": true, "cmd": ["/home/isucon/.xbuild/php-install", "5.6.13", "/home/isucon/.local/php", "--", "--with-pear", "--with-openssl"], "delta": "0:00:31.364152", "end": "2017-07-03 09:54:42.592654", "rc": 1, "start": "2017-07-03 09:54:11.228502"}
==> default: stdout: Start to build php 5.6.13 ...
==> default: php-build failed. see log: /tmp/isucon-php-install.log
==> default:
==> default: FATAL: all hosts have already failed -- aborting
==> default:
==> default: PLAY RECAP ********************************************************************
==> default:            to retry, use: --limit @/root/playbook.retry
==> default:
==> default: localhost                  : ok=14   changed=8    unreachable=0    failed=1
The SSH command responded with a non-zero exit status. Vagrant
assumes that this means the command failed. The output for this command
should be in the log above. Please read the output to determine what
went wrong.