If you assume a phone gets replaced every 3 years -- with service -- that's about $110 per year, or close to 7% of a person's total income.
In the US, median income is ~$32k -- $26k after taxes. If you make the same assumptions, a phone would cost about $580, or close to ~2% of a person's total income.
So it seems like not so big of a deal, especially for something so valuable.
But the teen part is what piqued my interest. India is MUCH younger than the US. Women participate in the workforce at a MUCH lower rate. And household size is MUCH larger. If you factor all of those things together, it means that for like 60% of families with children, you have a single earner with a spouse and 2.9 children. If everyone's got a phone, that's more than 40% of your household income. THAT seems insane.