How do you delete your iCloud email address?

I've bought a new phone and I have a new number. I want to sell my iPhone 5s and I'm going to get it unlocked. Before I cut the SIM card, I went on to sittings and erased all contents and settings. Do you think if I sell it, someone will still be able to access my email, photos and mobile numbers?

No they won't. If you erased all content and settings then it removes every bit of your data from the device. For someone to have access to that, they would need government grade software to extract data that hasn't yet been written over. This is something that 99% of the population won't have access to and I highly doubt your data is worth that much to them either.

It it was a full "factory reset" so it started up again like a new phone, everything has gone.

No one can access anything that was previously on it.

Make sure you totally disconnect it from your Apple account, otherwise a new owner can't use it.
See the instructions here