Seems unlikely given the differences in usual usage environments between a phone and a tablet; a phone is much more likely to be in environments where high water and dust resistance is desirable.
Apple can charge that iPad $4k. Would you pay for it? IP68 is not something that can just apply. Unlike iPhone, iPad is not generally used in places with exceedingly high humidity (tho in that case iPhone should not be used anyway).
On top of that, IP certification costs a lot. Design may need to change. I’m no designer but such change needs to be justified enough before diving in.