It depend on the make model of the phone.
Android phone, use you gmail account and back up to that
Welcome to the Community, as J0hn has mentioned, how to backup the contents on your phone depends on what phone you have, let us know and we'll be able to give you a more specific answer.
There are also third party cloud services you can use to backup any additional data like large folders of pictures / videos, like Google Drive or even [Virgin Media Cloud] if you're a media customer
I hope this helps
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