I really, really doubt there is an universal symbol because normally a symbol itself needs to include some specifics about the philosophy or content.
But let's try to make one.
I am trying to make it without a specific style. This style can be defined later.
To compare what I mean by style here is a google search about another "sphere" of humans, a "social sphere". Currently, this search is dominated by social networks logos, but you can find some that represent social by using several persons together. https://www.google.com.mx/search?q=social+icon&rlz=1C1GKLA_enMX664MX664&source=lnms&tbm=isch&sa=X&ved=0ahUKEwj5kPnY2r_YAhWL8oMKHYEkA8UQ_AUICigB&biw=1920&bih=1012
Here is a couple of rough icons using that idea to define a "style".
A "spiritual sphere or plane" could complement, let's say a physical or biological plane, emotional plane, intellectual one. So here are some that potentially illustrate those planes.
And a spiritual plane normally includes some kind of transcendental plane. Some specific philosophies can call it "Illumination", and some others can represent this in some form or another of "light". So we can probably use this as a starting point.
Depending on the philosophy behind it, this illumination can be from a "soul" based on the heart (E) or more "mind based", in the head (F).