Do nothing lamda...

$privilegeStrings = array_filter($privileges, function ($s) { return is_string($s); } );

Is there a better way to specify that I want just the string values in the given array?

You could do:

$privilegeStrings = array_filter($privileges, 'is_string');

array_filter passes every value of the array to the specified function. So you can just specify the function name and everything will be taken care of.

Reference

StackExchange Code Review Q#1129, answer score: 11