S5 is defined as the system extended from system K with the S4 schema $\Box \phi \rightarrow \Box \Box \phi$ and the S5 schema $\phi \rightarrow \Box \Diamond \phi$.
I'm trying to show that the axiom schema $\Box \phi \rightarrow \phi$ is independent from the rest of the axioms of S5. i.e. that S5 does not prove all instances of the schema $\Box \phi \rightarrow \phi$.
I have soundness of S5. And in classical logic to show independence of axioms, you would just create a countermodel and then apply the contrapositive of soundness to show a formula is not provable. But in this case, doesn't every S5 model satisfy $\Box \phi \rightarrow \phi$?
Assuming my clarification in the comments is what you intended:
Consider a Kripke frame with a single world $w$ and no accessibility ($w$ is not acessible from $w$). Then at $w$, $\square \varphi$ holds vacuously for all $\varphi$. It follows that all instances of 4 and B are valid on this frame. But T is not valid on this frame. For example, suppose $P$ does not hold at $w$. Then since $\square P$ holds at $w$, $\square P\to P$ is false at $w$.