phongo_manager_init currently has:

manager->client = php_phongo_make_mongo_client(uri, driverOptions);
mongoc_client_set_error_api(manager->client, MONGOC_ERROR_API_VERSION_2);

if (!manager->client) {
	phongo_throw_exception(PHONGO_ERROR_RUNTIME, "Failed to create Manager from URI: '%s'", uri_string);
	goto cleanup;
}

In the unlikely event that php_phongo_make_mongo_client returns NULL, mongoc_client_set_error_api could segfault before we throw an exception. In practice, this does not happen because mongoc_client_new_from_uri only returns NULL if SSL is requested but not enabled in libmongoc and we throw for that case earlier; however, this could change if a new error condition is introduced into libmongoc.