I don't think you need a PhD, although turns out many people I have met as Quant Strategists at the IB's have a PhD in Finance.
From my understanding of a QS at an IB, it's mostly prototyping and building of strategies from the group up. The programming skills have to be very strong possibly now as banks dont like having a separate programmer to implement your strategies.
But I could be wrong. It would be very hard to get straight into a QS position out of school with a Masters, unless you're very good, which you might be!