You would receive a bill from custom department by formal mail.
This custom clearance is done at the port of package entry.
I am not sure why it is Bombay for you. It should be Delhi international airport, if the address on package is Delhi.
2. Courier company contacts buyer
The second point to note is that the mail courier takes care of the package clearance formalities.
Normally, if your friend used a Fedex or UPS as courier, they would themselves get the custom clearance done (without you visiting the post office or custom office).
They will just give you a call to notify and submit some verification documents and then take care of the process.
If the Courier that your friend used in UK does not have any business partner in India, they would normally hand it over to ‘India Post’ for delivering.
You then need to visit the ‘India Post’s’ international package office (in Delhi, you should visit the ‘Foreign India post’s’ post office. I think it is in Kashmere Gate (Near state bus stand)).
Normally, you would visit the ‘Foreign Indian Post Office’ in your city to pay the amount and then they would release the package.
Everything will happen formally and you would receive the bill as well as the receipt.
Do not pay something to someone without any proper authenticated bills.
Here are the details of complete custom process along with documents when somebody send used mobile from US to India using Fedex: