initial uncompensated Phase is -179deg, for whole freq band it is negative as well around ,
what is the reason behind and what value we should use initially to compensate for , R, C without affecting BW.
Compensation would always reduce the bandwidth since it makes one pole more dominant and moves the other pole(s) more non-dominant. So bandwidth would always be less.
If you want to have the same bandwidth as the uncompensated one, you would have to increase the current.
For a simple Miller Compensated Amp, UGB is gm/Cc. So you would need to increase the tail current to increase gm which would increase your bandwidth.
You cannot reduce Cc since it is what achieves the pole splitting and gives you the Phase Margin.
Of course there would be other techniques where you can not burn a lot of extra current and still have a stable loop, but this one is the simplest and hassle free.