I see this structure in many literature
What structure do you refer to?
why do you assume circuit really unstalbe?
In your first post you said that in transient analysis you noticed instability at the output signal,is this true or not?
What kind of instability,common mode or differential?
It would be a good assist to us if you show us your testbench with details for transient analysis and a plot of the output signal.
Additionally what kind of filter is the one you design?Active-RC,OTA-C...?
What will need to do if phase response incorrect?
If you indeed designed an unstable filter,you can take some information from the phase response as LvW said and a pole-zero analysis of your circuit
will show a definetely good image of what is really going on.
For example,you may observe from PZ analysis that you have poles in the RHP so you must find a method to move them to LHP or
perform some kind of compensation.
In another case you may have instablity if you inject a common mode signal in your filter.In this case you must investigate what is going at the inside structure of the filter (at the opamp let's say for an Active-RC implementation or at the buffers etc.)
Provide more info to assist you further.