Is it permissible to posess in one’s house, etc… Tefillin and Mezuzot which have not been checked (may or not be posul) but are not being used at all (i.e., just being stored in a drawer, etc…) ?
You can have the tefillin or mezuzahs in your home. If you know that they were once kosher, then it is surely not an issue. Even if you got them and you don’t know if they were ever kosher, just write on it that you don’t know if they are kosher. This way there won’t be any concern that they might get used if they are posul.