As a general rule my practice is not to check tefillin and to rely on the chezkas kashrus.
I recently inherited a pair of tefillin. The owner passed away at the beginning of the pandemic, so it definitely had not been worn for over a year by the time I received it. Additionally, it most likely had not been worn for some time before that (possibly 10-15 yrs). However they were worn regularly at some point and there is no specific reason to think they became passul. The battim themselves look fine and undamaged to me, though the paint is a little puckered.
Lehalacha do these tefillin need to be checked?
It is definitely the correct approach to have the tefillin checked out. They weren’t worn for a long time and laying for a while could have caused mold of other things to happen to them over time. Additionally, you don’t know the quality of the tefillin, and they are quite old. Therefore, this is the correct thing to do.
O:CH 39-10, M:B 39-27.