With a score 450 in quantative, you'll not get a single admit in CS , let alone PhD.
But let us assume you tried to write (Q-700, V-450, A-3.5 ) . Most of the universities require 500 in Verbal for PhD in CS. Check the websites of some universities.Some of them require 4.0 in analytical section . It is their minimum requirement not the average mark . And also most universities accept students with a high CGPA for their PhD program .So if your CGPA is 3.1 or 3.2 , it'd be really risky for you to get an admit in PhD in CS. Besides PhD in CS require other things than GRE and CGPA.
By the way where are you doing your MS , US or other country ?
If you really did not appear GRE yet, then my suggestion is "DONOT PREDICT in GRE".
it is not like other exam we CS people generally face . I want to say more about this topic, but i feel tired now . Probably next time . Mark my words, you'll understand when you give GRE and apply universities .
I tried several post like you did here in the previous year after my GRE. But did not get a single reply . Thats why I am replying your post. Hope it helps.