Find which views are using Views PHP
Using the PHP filter in the fields should require you to use &lt;?php ?&gt; tags as part of the content.

The views data (unless its been exported with features) will sit inside the cache_views table in your DB, so you should be able to reliably find views using PHP filter by searching like so:

SELECT * FROM cache_views WHERE data LIKE '%&lt;?php%';

There is probably a more sophisticated way of finding this.. but hopefully its a good start!