In a smart phone there are usually two places where things are stored , the phones internal memory and the SD card so you will have to determine if your photos were stored on the SD card.
When you format any drive whether it be flash drive hard drive or SD card what ever is on it will not actualy be erased but will be set so that you can write over it. Formatting does not erase it just allows the data to be written over by other data that you put on the drive , so that the data is still there untill you write over it. This means that what ever is formatted can be recovered with the right recovery software.
That's depends. Normally, if you save your photos on the phone, formatting the SD card often cannot delete them. But, if you save them on the SD card, they will absolutely be deleted after the formatting process.
As inzone said, it is possible to recover the images if you format it - but only if you don't write anything to the freshly formatted SD card.
It's kind of like carbon paper if you've ever used it.
There's two pieces of paper. Writing on the top sheet will make an impression on the bottom sheet. Formatting would be comparable to putting white out on the top piece - the information would still be on the sheet below.
However if you were to then write on it, it would be imprinted overtop of the original on the bottom sheet. You would be unable to read any of it.
To save yourself the trouble of having to find a data recovery software to get those images back for you if you were to format it, I'd recommend just saving all the pictures to your PC first.