According to Debian people, "PHP License (any version) is suitable only for software that comes directly from PHP Group", while extensions such as Numbers_Words do not fall under this group. Thus, the code under the PHP License cannot be distributed with Debian. The full reasoning and discussion can be found here: https://lwn.net/Articles/604630/. Please consider relicensing the source in order to allow its modifications and their distribution.
Similar issue in Net_FTP, which was resolved by relicensing the source as BSD: https://pear.php.net/bugs/bug.php?id=20317