How can I find the PDF of $z = \exp(j\varphi)$, where $\varphi \sim \mathcal{U}[-a, +a]$?

My difficulty here is that it involves complex numbers and I don't know how to handle it.

How can I find the PDF of $z = \exp(j\varphi)$, where $\varphi \sim \mathcal{U}[-a, +a]$, $i.e.$, a uniformly distributed r.v.?

My difficulty here is that it involves complex numbers and I don't know how to handle it.