two way transfer between iPHONE & laptop done automatically?

Apple's iTunes software is, in the main, designed to transfer data from the computer to their devices but not in the other direction. You are right, if you try to sync you will lose the music on your iPhone. For more info and possible solutions, see:

Recover your iTunes library from your iPo… - Apple Community

iTunes sync IS NOT A TWO WAY PROCESS. This IS a definitive reply.

If your device has content or playlists that aren't in your library then it is possible to reclaim that material, but you cannot rely on iTunes to do it for you automatically. What generally happens if you try to sync an iPhone to a new (to it) library is that all media and playlists on the iPhone are removed and then replaced with the content from the local library. The workarounds are discussed in Recover your iTunes library from your iPod or iOS device - Apple Community. It is long and complicated as it attempts to address multiple scenarios and potential gotchas in one place so you don't have to come back and forth asking for more information. That said I am more than happy to try to help further if I can. As above, the simplest method seems to be to use a brief subscription to Apple Music's subscription service to merge the content and playlist from the device into an iCloud Music Library that can then be downloaded to your computer and backed up. In the process the library on the computer gets all of the songs and playlists that are on the device, and the device will get any new unique content that is currently on your computer. Make sure to merge and not replace the content on your iPhone when signing up for Apple Music.

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A temporary subscription to Apple Music may allow the content on your phone to be synced to your computer. Download everything to the computer and backup the library before you allow the Apple Music subscription to lapse.

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