Your 200GB iCloud storage quota (corresponding with your £2.49 monthly subscription) is shared across all devices that share the same AppleID - and for higher storage tiers, can also be shared with others using Apple Family Sharing.
You can see precisely how much of your iCloud storage is being used from your device:
Settings > [Your Name / AppleID] > iCloud
At the top of the settings page you will see both your current storage quota - and the amount of iCloud storage currently used. If you tap Manage Storage, you can see more detail and a breakdown by individual Apps. Here you can also manage your iCloud storage subscription; tapping the Change Storage Plan link will take you to a page where you can upgrade or downgrade your monthly subscription.
More information here:
Manage your iCloud storage – Apple Support