How to plug my iPhone in the computer with out getting music deleted?

I have an 2 iPhones, I buy music on I tuneson my phone, and it's been a long time since I plugged it into my computer, then I plugged one iPhone in to download this movie, but when I plugged it in, it deleted all my music. And I want to plug in the other phone in, but not sure if it will delete too. I tried downloading the same music in iTunes pc, but I have to pay again. What do I do?

You should put your musics inside your PC before adding them into itunes. Make a backup folder first. This might be caused by some ghost files or jailbroken model.

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