I have to agree that if your phe levels are regularly between 7 and 14 mg/dl while eating 325 mg of phe it could be that this is too much phe for your body. Talk to your doctor and/or dietitian about experimenting with your phe intake and seeing what happens if you lower your intake a little bit.
It also might help to split your meals up into 3 low protein meals and a snack each day rather than consuming all of your phe in one meal. For example rather than eating 325 mg of phe once a day try eating three meals with approximentally 100 mg of phe per meal, and then have a low protein snack to make up for anymore phe left during the day.
I'm only nineteen, have not been pregnant before, and do not plan to be pregnant until the distant future, but it's my understanding that the majority of your nutrients for yourself and your baby during pregnancy comes from your formula. Take a look at the label for your formula when you have the chance. It is packed with calories, vitamins, minerals, and amino acids (minus phe of course).
If you haven't already sit down with your doctor or dietitian and see if they have any suggestions. I hope this helps.