GPA for PhD application
Two Bs in significantly harder, graduate level classes will not harm your chances of admission much if at all. Your GPA will only take a very slight dip from them (assuming your other marks are high) and, really, you did fine for your level. Remember that you are a whole package, not a just GPA. Write a good statement of purpose, work on doing well on the GREs if you are talking about the US, and do some volunteer research assistance to pad your CV. You're fine!