# Understanding the FFT phase spectrum with a simple example

I'm trying to compute the DFT using scipy's functions. I don't understand why the phase spectrum of a simple sine wave with 2 Hz frequency doesn't show $$\pm\pi/2$$ at the $$\pm 2Hz$$ frequencies. Instead, the phase plot seems to have some linear dependence in the frequency, which I don't understand. I provide the code for assistance. How can this be fixed? Looks like a simple issue I'm not grasping. Please help.

import numpy as np
import matplotlib.pyplot as plt
from scipy.fftpack import fft, fftfreq

# 1Hz sine wave
npts  = 100
tmax  = 10
t     = np.linspace(0, tmax, npts)
y     = np.sin(2*np.pi*2*t)
dt    = tmax/npts

# FFT computation
Y      = fft(y)
freq   = fftfreq(npts, d=dt)
amplit = abs(Y)/npts
phase  = np.angle(Y)
phase  = phase / np.pi

fig, ax = plt.subplots(1, 2, figsize=(10,4))
ax.plot(freq, amplit)
ax.plot(freq, phase)

ax.plot([2,2], [0,0.5], '--')
ax.plot([-2,-2], [0,0.5], '--')
ax.plot([2,2], [-1,1], '--')
ax.plot([-2,-2], [-1,1], '--') 