Here is one way to get the spectrum.
clc, clear
% fundamental frequencies
f1 = 1/3;
f2 = 5/6;
% sampling frequency
fs = 50*max([f1, f2]);
% sampling period
Ts = 1/fs;
% Time span (5 periods)
T = 5*max([1/f1, 1/f2]);
% time axis
t = 0:Ts:T-Ts;
% frequency axis
f = -fs/2:fs/length(t):fs/2-fs/length(t);
% signal
x = 2 + cos(2*pi*f1*t) + 4*sin(2*pi*f2*t);
% fft
X = fftshift(fft(x));
% figure
fig = figure('Units', 'normalized', 'Position', [0.15 0.35 0.75 0.55]);
% plot signal in time
subplot(1, 3, 1), plot(t, x),
xlabel('Time (sec)'); ylabel('Amplitude');
title('Signal'); grid 'minor';
% plot fft magnitude
subplot(1, 3, 2), plot(f, abs(X)),
xlabel('Frequency (Hz)'), ylabel('Magnitude'),
title('Spectrum, magnitude'); grid 'minor';
% plot fft phase
subplot(1, 3, 3), plot(f, unwrap(angle(X))),
xlabel('Frequency (Hz)'); ylabel('Phase');
grid 'minor';
title('Spectrum, unwrapped phase');
