bz2 is installed and enabled, but phpMyAdmin does not offer 'bzip2' support for export compression. Only none, zip and gzip are offered.
BZip2 Support Enabled
Stream Wrapper support compress.bzip2://
Stream Filter support bzip2.decompress, bzip2.compress
BZip2 Version 1.0.5, 10-Dec-2007
BZip2 Support Enabled
Stream Wrapper support compress.bzip2://
Stream Filter support bzip2.decompress, bzip2.compress
BZip2 Version 1.0.6, 6-Sept-2010
Support for .bz2 compression was withdrawn due to bug 4221 [1]. Also see this mail thread [2] from developers' mailing list.
[1] http://sourceforge.net/p/phpmyadmin/bugs/4221/
[2] http://sourceforge.net/p/phpmyadmin/mailman/message/31848153/