will my rank remain the same if I don't write phase 2??
I don't know which exam you are talking about. But in general, if the phase-2 isn't compulsory then your rank will not get tampered. For this case, if you attempt the phase-2 then the best of the two phases will be taken as your final results. Now if the phase-2 is compulsory then your rank may get reduced.
I hope my answer helps. All the very best for your future endeavors!