I have 2T extra memory in cloud, why my phone does not have space ?

There are three major advantages of having iCloud Storage

1. iCloud syncs your iPhone data and keeps backup safely for future use if your iPhone is damaged or lost. The data is safe on iCloud
2. You can save space on your iPhone by keeping low resolution photos on iPhone and keep the originals on iCloud. When ever you open a Photo on iPhone it will fetch the original photo from iCloud and display it to you, provided you have internet. --> Manage your photo and video storage - Apple Support
3. You get more space on iCloud Drive and keep any file on it safely, Also you can view and delete them from any device.

iCloud Drive is part of iCloud Storage. What you store in iCloud Drive counts against your storage limit.

See the pic below. These are thing which you can view. There are many thing which you can't view such as messages, backup, message attachments etc..

Because the 2T storage capacity is in iCloud and not in your iPhone. Please read SrafanKrA's post to find ways to reduce the items stored in your iPhone and free up storage on the iPhone. Having 2T in iCloud will not increase the original storage capacity of your iPhone.