Q: my old laptop died what happens if i plug in my iphone to new laptop with new itunes

take a look at this article by one of our users.

Syncing to a "New" Computer or replacing a "crashed" Hard Drive

Your i-device was not designed for unique storage of your media. It is not a backup device and media transfer was planned with you maintaining a master copy of your media on a computer which is itself independently backed up against loss.  To use a device with a different setup you transfer the old library from a computer or a backup directly to the new setup, not the device to the library. Media syncing is one way, computer to device, updating the device content to the content on the computer, not updating or restoring content on a computer from a device. The exception is iTunes Store media purchases which can be transferred to a computer.

Redownload or transfer your iTunes Store purchases from an iPhone, iPad or iPod to a computer - https://support.apple.com/en-us/HT201267 - "This feature works only for content bought from the iTunes Store." As of iOS9 it no longer does apps which now must be re-downloaded directly from the Store.

For transferring other items from an i-device to a computer you will have to use third party commercial software.  See this document by turingtest2: Recovering your iTunes library from your iPod or iOS device - https://discussions.apple.com/docs/DOC-3991  Even this method may not fully recover what you had in the library originally. For example if in order to save space when syncing you had converted music files to a lower bitrate, or photos to a lower resolution, it is those lower quality files you will recover.

If you subscribe to Apple Music, tracks which are not part of content you have purchased or uploaded cannot be transferred and have to be downloaded directly from iCloud.

missmaffews wrote:

My old laptop has died which has the back up of my iphone on the iTunes. What would happen if i plug in my phone to the new laptop with a newly downloaded iTunes. I dont want to lose any data on my phone...

You should not lose the data currently on your phone. When you connect the phone to the new laptop it will ask you if you want to set it up as new. Chose new, it will not wipe your phone (it is confusing I know). See the response by  ozZySPL  here:  itunes "set up as new ipad" question

You should be able to backup your phone to your new laptop. You should be able to import photos on your phone to your new laptop. For other material, Limnos gave you a great explanation.