This is how Ebay's return policy works and it does favour the buyer.
There is no advice to give - the buyer found a feature of the phone did not work so they opened a case.
You really have no choice but to accept the return and Ebay give buyers a fairly lengthy time to return items.
The buyer has not done anything wrong here but many sellers find Ebay's policy unfair.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)