Missing methode in mongoDB methode


I’m using the official Yii2 docker container for an Yii2 application with mongoDB.

The mongoDB extension works out of the box, because the docker image contains all needed packages (PHP mongo extension, etc.).
But it looks like, the implementation is not complete. Especially for the methods provided by the mongoDB PHP extension ( PHP: MongoDB - Manual ): not all methods are available.

For example \MongoDB\BSON\toPHP and \MongoDB\BSON\fromJSON is not available:
[Error] Class 'MongoDB\BSON\fromJSON' not found
while \MongoDB\BSON\UTCDatetime is available and works.

I reinstalled / recompilled the mongodb pecl module, but no change.

Any idea, how to get all BSON-methodes (PHP: MongoDB\BSON - Manual) accessible and running?