It appears you have 2 AC sources on at the same time.  Try turning off the AC signal on source V28.

By seeing your gain-plot and phase-plot, I think you are desinging a high gain amplifier. A high gain amplifier, more than 100dB, the first pole may at "negative-frequency" when you apply compensation capacitor. So, if the first pole at negative-freuency your phase-plot is not start from 0deg or 180deg. But this is not the only reason that your phase-plot isn't  start from 0deg or 180deg. You can check the gain-plot and pahse-plot near dc  frequency, there maybe a RHP-zero at dc frequecy. You should still check that too.
Hope you are doing well.  :-?

Thank you Aaron & Tiger_ITRI. I plotted frequency response down to a much lower frequency . Graphs are attached but I’m unable to understand that response .

Thank you

Yes, you can trying STB analysis and compared these two simulation result.
By the way, if a amplifier is designed rail-to-rail input stage, there maybe zeros at frequency spectrum.

Never, ever, try to simulate loop gain by breaking the loop. It always gives the wrong answer. There are many creative ways to break the loop: using extremely large capacitors and inductors in the feedback loop is one of those ways. People try to tell themselves it is okay because it only breaks the loop only during AC analysis, but the result is the same: no conclusions can be drawn about the stability of the circuit because you changed the circuit. The results of this simulation is meaningless.

If you are using Spectre, learn to use the stb analysis. If using some other simulator, read http://www.kenkundert.com/docs/cd2001-01.pdf and implement it in your simulator.

-Ken

Hi, aaron_do:
The meaning of that I mentioned before is if an amplifier is high gain, such as more than 100dB, these amplifiers may be desinged by applying cascaed techniques, such as chopper or chopper-stabilized, these techniques usually need higher level and robust compensation techniques such as nested-miller frequency compensation ,NMC ,MNMC...etc. By using that techniques, the dominant-pole is much lower than a gerneral operational amplifier, usually, affter compensation, the dominat-pole may not appear in positive spectrum, because it move to negative-frequency axis by milller pole-splitting theorem.
Have a nice day~

Hi, aaron_do:
I think I can agree with you. So, I should correct that I mentioned before. Please any one who visist this board, don't follow the concept that I posted before. Many thanks.