Try substr_count()
Here's how I go about finding functions: If you go to php.net, on the search, type in string functions and click the online documentation option from the drop down then search. Click the one that says Strings - Manual. That has a description of all the string functions along with their descriptions. The same goes for arrays and other functions you're looking for.
Hope this helps. It's saved me a lot of time.
Cgraz