There is a lot of confusion about this problem. It's a problem that applies to any prim attachment worn on the chest or moved to cover the chest. And it's not a problem you can deal with. People think they can solve this problem in two erroneous ways:
- I just won't use Phoenix
- I'll use Phoenix but disable breast physics
What is a real solution ? The only thing you can do is to edit the prim attachment so it is positioned slightly off of your chest and then thicken it as much as possible without distorting the look too much. My post on J's Lace-Up Bra has instructions on how to do this with J's hud. Other items will need to be edited manually. It is tricky and difficult but the only thing you can do aside from just not wearing prim attachments on your chest. This solution works well for my bra, corset, and bikinis but does not work for sculpted nipples as they really must be positioned close to the breast.
The only time I can wear my 3D sculpted nipples is when I know I will not be bouncing much - posing for photographs, sitting, etc.