One uses it because it is generally used; there is no justification in using that particular word in relation to some outer manifestations rather than to all.

Properly speaking, "phenomena," of course, will cover the whole of the objects in the world, in the Not-Self, everything outside the Self; but the word has been narrowed down, especially in our own time, to those occurrences in the world around us, in the Not-Self, which are unusual, which seem to be abnormal, which are the results of laws which are not familiar, and therefore which are regarded by some people as supernatural, by others, speaking more carefully, simply as superphysical.

And we lose much by separating off what we call "abnormal" happenings, the so-called "phenomena," from the normal every-day happenings of life.
For there is no fundamental difference between them.

All planes are equally within the realm of law; all worlds, denser or grosser in material organisation, are equally worlds moving by order and law.
There is nothing really abnormal in Nature.

Some things happen more seldom than others--are unusual; but the very idea of abnormal seems to me in many respects mischievous and harmful.