Hmm...maybe you're right. I just checked Apple's Tech Specs pages for both the iPad Pro 11 and the iPhone 11 Pro and there *is* a significant difference between the PPI numbers (264 PPI for the iPad, 458 PPI for the iPhone), which surprises me. One would think that if Apple didn't think there was *some* value in going from 264 to 458, they would save themselves (and consumers) some amount of money and battery life by using a lower-res screen on the iPhone.
Although it's also possible that a significant factor is just for them to use it as a marketing advantage when comparing against Android phones, for example.
Still, I'm looking at my older 9.7" iPad Pro (also 264 PPI) right now, and I have good near-vision and I really can't make out any pixels. Fonts look razor-sharp to me.