mongod --version
db version v3.2.8

php -i | grep mongo
 /etc/php/7.0/cli/conf.d/20-mongodb.ini,
 mongodb
 mongodb support => enabled
 mongodb version => 1.1.8
 mongodb stability => stable
 libmongoc version => 1.3.5
 mongodb.debug => no value => no value

sudo pecl install mongodb

pecl/mongodb is already installed and is the same as the released version 1.1.8
install failed

sudo pecl uninstall mongodb

sudo pecl install mongodb

<?php

echo "I am here";
$connection = new Mongo('localhost');
$db = $connection->mydb;

$list = $db->listCollections();
foreach ($list as $collection) {
    echo "$collection </br>";
}

echo "I am never here";
?>