Send Phone bought in India to India back from USA with Indian Amazon receipt?

Do I still need to pay custom duty tax on phone bought from India?

I want to sent Indian bought Phone from USA to India. I bought OnePlus Phone in India, now I moved to USA.

I bought new phone here and want to send my old OnePlus phone back to India.

I have bill also.

Sending used phone bought in India back to India from abroad

You will still have to pay customs duty. I do not think the Indian bill will be honored by customs.

Indian customs allow declaring products while leaving India

The normal practice is to declare and get a receipt from Indian customs at the time of leaving India, when somebody carries extra phone (or laptops) abroad. They can then show it to customs when they return to avoid the otherwise applicable duty on imports.

Now, in your case, you do not have that receipt from Indian customs that you brought this phone from India to US.
And second, you want to send it by post to India.
It is not possible to prove that this phone is what you brought to US and now sending back to India.

I have not heard of any case which may have skipped custom duty with same scenario.