If I sync JUST music to iPhone on a new computer - do I lose everything?

Hi, my computer is broken and in for repair but I want new music on my iPhone. If I plug my iPhone into my laptop (after unticking 'allow devices to auto-sync') and ONLY sync music… Will I lose everything on my phone or will my music just change?

It suggests in a warning I can only sync to one computer and I'd lose everything - but I don't know if this 'everything' is actually everything - like my pictures - or just all my current music - which would be fine.

Thanks in advance.

Plug it in, don't let it sink. Click file, then you can back up your stuff on your iPhone!