If I have a 1TB storage Iphone, do I still need icloud ?

Icloud services 2 primary purposes. It serves as storage for your device backup file. And it serves as a synchronization service to sync content across devices (e.g. messages, notes, contacts, calendars, photos, documents for apps, etc).

Synchronized data lives on all devices using that iCloud account, as well as on each device itself.

So if you have other Apple devices and sync a lot of content via iCloud, then the amount of storage on your device does not change that (other than you can now sync a lot more data).