Why do I get the wrong phase after I apply FFT to my sinusoidal?

I have a function x = A0*(1+sin(w*t + phi)); all the variable are known. The time vector is provided also. When I take a vector of the solution x do an fft on it, I get the wrong phi that I started with. For example, my phi = 45, I get back 180. Here is what i have so far:  
    x=[.....]; 
    t=[.....];
        m=ceil(log2(length(x))); 
        fft_A=fft(x,2^m);
        fft_A = 2*fft_A/length(x); 
        %Find the phase angle
        FT_power2 = abs(fft_A).^2;
        FT_phase2= ((unwrap(angle(fft_A))))*(180/pi);
        [c2,i2] = max(FT_power2);
        phase = (FT_phase2(i2))

What am I doing wrong? thank you.
PS: I understand that I have a DC offset of A0 but I am not sure how to deal with it and what to expect.

[Nina]

I believe my issue is finding the correct bin where the amplitude and phase would fall into, is there a general way to do that if you supposidly do not know the information before hand ?(i.e frequency,amplitude...)

[Matt J]

You asked effectively the same question here (and received answers)

http://www.mathworks.com/matlabcentral/answers/59118-not-getting-the-correct-phase-using-fft-code-posted