I am running Debian testing.

I made a fresh install of lighttpd and did not change its configuration or enable any modules.

Then I installed phpmyadmin and asked it to configure automatically for lighttpd. This caused lighttpd to be unable to start. I checked the log and found this message:
Jan 06 08:44:06 saturn lighttpd[339062]: /usr/bin/php-cgi: No such file or directory
Jan 06 08:44:06 saturn systemd[1]: lighttpd.service: Main process exited, code=exited, status=255/EXCEPTION

I think that this is because the postinst script in the phpmyadmin package enables the lighttpd fastcgi-php module:
lighty-enable-mod phpmyadmin auth fastcgi fastcgi-php
But this module needs to have /usr/bin/php-cgi available, and phpmyadmin doesn't depend on the php-cgi package.

Note, though, that the description for the php-cgi package says this:
"Note that MOST users probably want the php-fpm package that provide FastCGI support."
So I think that, rather than phpmyadmin adding a dependency on php-cgi, it would be better for phpmyadmin to add a dependency on php-fpm and enable the fastcgi-php-fpm module in its postinst.

Let me know if I can provide any further information.

Thank you,
James Dietrich

While the workaround for this bug is fairly straightforward (apt-get
install php-fpm), this doesn't negate the fact that this bug makes
"apt-get install mysqladmin" cause lighttpd to fail and refuse to start
up.  It also caused the initial install to fail and left the package in
a partially installed state.

When installing one package causes another, a major subsystem at that,
to fail, I would recommend the severity be at least "serious".