I know it is possible to delete a phone entry because I had to delete my SA's phone from my car. I just had to dig through my memory since it has been a while. A quick review of the Good To Know app pointed me in the right direction. Porsche seems not very consistent in how to change various settings in the car. Sometimes you push this button, sometimes you push that one, sometimes you touch an on-screen button, sometimes you just raise your left hand and whistle.
Resetting the PCM won't do it. If it did it would also forget all the connections you want to save. And the Device Manager, which I suggested earlier, seems to be about managing the entries which exist, not about changing them.
The way to do (I think, without doing it again myself) it is to bring up Phone from the Home screen and push the Opt button. You may also be able to push the Opt button from the Device Manager screen. From there you may have to push some other buttons, such as select an entry and first and touch delete, or raise your left hand and whistle.