I don't think this reads correctly, you shouldn't start a new sentence with "Where". We should keep this short and simple, I really preferred this:

    If the object contains phenomenon values it can be a numpy array
    or array subclass, or any object that is convertible to an array using
    :func:`numpy.asarray`.

because it doesn't get too complicated, just an array or anything that is like an array, the following would be fine too:

    If the object contains phenomenon values it can be a numpy array
    or array subclass, or an *array_like* as described in
    :func:`numpy.asarray`.

Remember that the reference to `numpy.asarray` will be turned into a link to the numpy documentation for that function in the online iris documentation, so users should have no problem finding what they need.