About zero-padding for the FFT in the Matlab

I have a question about the zero-padding for the fft. I ran fft with zero-padding & without zero-padding and compared.

sf = 100; %sampling frequency
dt=1/sf; %time sampling interval
L = 10; %Length of signal
t = linspace(0,L,L/dt+1);

%zero-padding
nfft = 2^nextpow2(length(t)); %expansion of the data length for fft
t(length(t)+1:nfft) = 0; L = dt*nfft; t = linspace(0,L,L/dt+1);
t(end)=[];

fr = 4; %frequency
data = cos(2*pi*fr1*t);
df = sf/length(data); %frequency increment
f = (0:length(data)/2)*df;
fft_result =fft(data)/length(data);
spec_fft = 2*abs(fft_result); %spectrum
pha_fft = angle(fft_result); %phase
pha_fft = rad2deg(pha_fft);

subplot(2,1,1);
stem(f,spec_fft(1:length(f)));
subplot(2,1,2);
stem(f,pha_fft(1:length(f)));

And I could see the difference between the two result images.

When I did fft without zero-padding, the amplitude was displayed clear, and the phase also clear (I think other frequencies' phase is due to a very small amplitude value not zero). But When I used zero-padding, I could see amplitudes of nearby frequency that I input(4Hz) show different aspects and the result of the phase is strange in my opinion. Is there some problem in my code when I used zero-padding?

*Additional question for comments of Cris Luengo

I tried to pad zeros to the data by the extended length.

nfft = 2^nextpow2(length(t)); %expansion of the data length for fft
data(length(t)+1:nfft) = 0;

When I plot the data, I got As you can see, values over 10 are zeros.

And I got this result.

I wonder whether my results are okay or not.

If the FFT magnitude result is close to zero, it might just be numerical noise (random quantization and rounding errors). The phase of this numerical noise is nonsense. I usually set the phase to zero unless the corresponding magnitude is above some threshold for actual non-zero spectrum.