Quoting jesse in CDRIVER-1110:

By the way I notice a "FIXME" in Phongo to deal with a NULL return from mongoc_collection_find_with_opts – that can never happen, mongoc_collection_find_with_opts always returns a cursor.

Remove the following code from phongo_execute_query():

/* mongoc issues a warning we need to catch somehow */
if (!cursor) {
    phongo_throw_exception(PHONGO_ERROR_MONGOC_FAILED TSRMLS_CC, "%s", "FIXME: Couldn't create cursor...");
    return false;
}