This only works if both parties are on the same PSP and no VPA lookup over UPI is required. So if I am not registered on PhonePe, you can’t send me money using

This only works if both parties are on the same PSP and no VPA lookup over UPI is required. So if I am not registered on PhonePe, you can’t send me money using just my phone number there. For other cases, most PSPs will automatically register mobile@psp for you with an opt-out.