Phase of the sine signal by finding FFT of it in matalb using angle
The basis function for the Fourier Transform is the complex exponential $e^{j\omega t}$
Since
$$sin(\omega t) = \frac{1}{2j}(e^{j\omega t} - e^{-j\omega t}) $$
the Fourier Transform of a sine wave a phase of -90 degrees at the positive frequency and a phase of +90 degrees at the negative frequency.
For a cosine, the phase would be 0 for both the positive and the negative frequency.