Battery health

not necessarily.. you can have the battery replaced.

iPhone Battery Replacement - Official Apple Support

If you have an older model iPhone that cannot run iOS 14, then it would probably be a good time to consider getting a new iPhone though

Supported iPhone models - Apple Support

No, but it means you should have Apple replace the battery→iPhone Battery Replacement - Official Apple Support

kirstein161 Said:

"Battery health: My battery health is 77% does this means i need to buy a new phone"

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Time to Upgrade?:

No. But how old is this iPhone?. If more than 5 years old, then take this as a good chance in getting a new phone.