Shouldn't the surface $\phi=2\pi /3$ in spherical coordinates have a positive slope?

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That's a picture in my textbook. In spherical coordinates, $\phi$ represents the angle to the $xy$-plane. But the surface indicated in the picture seems to have $\phi = 4\pi /3 = -2\pi /3$, not $2\pi /3$. Am I misunderstanding something?

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Note that the angle $\phi$ is measured with respect to the $z$ axis, not $x$ or $y$. It covers a domain of $(0,\pi)$, where $\pi$ corresponds to the downward $z$-direction..

So, the angle $\frac {2\pi}{3}$ is correct.