I had some lithium ion batteries (I had a spare) on the bottom of an older macbook pro expand so much they burst out of their cases and actually raised the computer up onto an odd angle.
I actually took these back to the apple stores years out of warranty and complained that this was a bit of a safety issue since old batteries should just stop working, not expand like this and potentially explode. Apple was very good about it and gave me two new batteries worth a few hundred bucks at no charge. I was very happy.
So in short, expanding batteries could most definitely put pressure on other components on the phone and cause damage / weird stuff to happen