how do I backup iPhone to the cloud

Settings>> appleID>>iCloud >>iCloud backup

if the backup turned on,

backup your data automatically when you connected to power , locked and turn on WIFI (iPhones with 5G, you can use cellular network instead)

Hello ~ Take a look here…

How to back up your iPhone, iPad, and iPod touch

~Katana-San~

RJK323 Said:

"how do I back up iPhone to the cloud"

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About Backing an iPhone Up to iCloud:

Note that the entire iPhone does not get backed up to iCloud; Only certain internal data does: What does iCloud Back Up? - Apple Support