There is the packages.ubuntu.com website. It's pretty handy for this stuff.

Here is the current output:

lucid (php): server-side, HTML-embedded scripting language (metapackage)

5.3.2-1ubuntu4.20 [security]: all



lucid-updates (php): server-side, HTML-embedded scripting language (metapackage)

5.3.2-1ubuntu4.20: all



precise (php): server-side, HTML-embedded scripting language (metapackage)

5.3.10-1ubuntu3.7 [security]: all



precise-updates (php): server-side, HTML-embedded scripting language (metapackage)

5.3.10-1ubuntu3.7: all



quantal (php): server-side, HTML-embedded scripting language (metapackage)

5.4.6-1ubuntu1.3 [security]: all



quantal-updates (php): server-side, HTML-embedded scripting language (metapackage)

5.4.6-1ubuntu1.3: all



raring (php): server-side, HTML-embedded scripting language (metapackage)

5.4.9-4ubuntu2.2 [security]: all



raring-updates (php): server-side, HTML-embedded scripting language (metapackage)

5.4.9-4ubuntu2.2: all



saucy (php): server-side, HTML-embedded scripting language (metapackage)

5.5.1+dfsg-1ubuntu1: all

As of Xenial Xerus the keywords string to search is "php". (the version is PHP7)

xenial (php): server-side, HTML-embedded scripting language (default)

1:7.0+35ubuntu6: all

also provided by: php7.0



xenial-updates: Virtual package

provided by: php7.0



yakkety (php): server-side, HTML-embedded scripting language (default)

1:7.0+42: all

also provided by: php7.0