def phonenumbers(s):
    """Clean phonenumbers by removing all non-numbers (except +).

    Parameters
    ----------
    s: pandas.Series
        A Series to clean.

    Returns
    -------
    pandas.Series
        A Series with cleaned phonenumbers.

    """

    # Remove all special tokens
    s = s.astype(object).str.replace('[^0-9+]+', '')

    return s