Based on a clarifying comment, the question is why my phone is being used instead of his phone.
A clue to what's going on can be seen when looking at the sentence in the context of the story itself.
A link to Jennifer Cardoza's article "Rickshaw Kindness: Simple generosity can mean the world" shows that the story is written in the first person.
Here are the second and third paragraphs of the story:
I left my apartment carrying two bags, a handbag and a lunch bag, and boarded an autorickshaw passing nearby. As I walked to the bus stop, I realised I had only my lunch bag – I had left my handbag, containing two ATM cards, a new mobile phone and a sizeable amount of cash, in the autorickshaw!
It took me a few seconds to calm down. Here I was – without so much as a single cent to pay for my bus fare, no mobile to call for help and not a Public Call Office in sight. My work phone number was stored in my mobile so I couldn’t even ring to tell them about my predicament. To add to my woes, I did not have the key to my apartment either. I felt as though I was blindfolded in the middle of a forest.
Accessing the complete story, including the example sentence, requires signing up for an account on the website. But I don't believe I need to do that.
From the context, I either know or am assuming several things:
- Reader's Digest normally has autobiographical stories submitted by its readers. So, it's likely that the protagonist in this story is Jennifer Cardoza herself.
- Jennifer forgot her handbag in the back seat of a rickshaw.
- The use of my mobile in the example sentence refers to the mobile belonging to Jennifer—which is in her handbag.
- At some point in the story, Jennifer must call the rickshaw driver from some other phone to inquire about her lost handbag.
- Also at some point, somebody calls her—but the call goes to her mobile, still in the rickshaw.
- Another lady must have become a passenger in the rickshaw.
- In order for Jennifer to get back in touch with whoever called her mobile (still in the rickshaw), she tells the driver to instruct the new passenger to return the call.
- In order to return the call, the new passenger must use Jennifer's lost phone.
This is why my phone is being used, not his phone.