While part of the demand for large phablets is from developing countries due to lower device cost and power reliability, for other countries like China, the demand is because of different reasons. Consumers there aren't buying a $1,400 iPhone 14 Pro Max because it's their first computer. It's because Chinese consumers live far more digitally connected lives than in western countries.
For example, 80% of transactions in China use digital payment. The only people using credit cards or cash are seniors and visitors. Another example is livestream shopping where it is a $500B market in China vs. $10B in the U.S. Everything is digital whether you're talking about identity cards, parking tickets, or student report cards.
As more consumers around the world live digitally connected lives without needing to carry a wallet, their screen time increases leading to preference for large phablets.