How to make a waveform and identify the pahse of a signal?

Hello everyone!

I truly appreciate if someone helps me as I am realy a new MATLAB user. I have a small signal (only two samples)(attached) and I have made the amplitude spectrum and phase but my proffessor said the phase and waveform are wrong. Then, I need to make the waveform and identify the phase in time domain again. I ppreciated your points in advance! My code is below:

clc;
clear all;
close all;
data=xlsread('1');
amp=data(:,2);%us/f
time=data(:,1);%ms
t=time(1:1:end);
am=amp(1:1:end);
l=length(t);
NFFT=l';
S = fft(amp)/NFFT; 
P2 = abs(S)*2;
lP2=floor(length(P2));
mS=P2(1:lP2);
freqS=1:lP2;
figure(1)
plot(freqS,P2,'g','LineWidth',2);
ylabel('Amplituse (dB)','FontSize',14);
xlabel('Frequency (Hz)','FontSize',14);
xlim([-inf max(freqS)])
%.........................
PP=phase(S); %Phase Spectrum
figure(2)
plot(freqS,PP,'g'); %Plotting the frequency domain
xlabel('Frequency (Hz)','FontSize',14);
ylabel('Phase','FontSize',14);
%...............
fx=fft(am);
fx(50:350)=0;
X=abs(ifft(fx));
figure(3)
plot(X,'b','Linewidth',2) 
xlim([0 100]);
xlabel('Time (ms)','FontSize',14)
ylabel('Amplitude','FontSize',14')
title('Waveform','FontSize',14')