Excellent. First things first, apple most likely is going to replace the phone rather then repair it. So you want to make sure you make a complete back up of your contacts, photos, etc, using either itunes or icloud.. This link will show you how.
( even though the phone is acting funny, you can still make a backup) https://support.apple.com/en-us/HT203977
When you get the new phone, your going to restore that backup to the new phone, so that it loads all your current contacts, photos, etc.
Now, as far as requesting the replacement. Go to this link, https://getsupport.apple.com/
On that page click iphone, then click repair and physical damage, then click accidental damage, then click send in for repair, then click one of the three options to verify what phone you want to send in , and then follow the rest of the steps to arrange to send the phone in.
if you have further questions, let me know.
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