Are photos deleted from iPhone also deleted from iCloud?

Yes.

iCloud Photos is a syncing service. Any photo you delete from a device where iCloud Photos is turned on will also be deleted from iCloud and from any other device connected to iCloud Photos. You can potentially reduce the storage space required on a device by turning on Optimize Storage. See: https://support.apple.com/en-us/HT204264

Apple does not currently offer cloud-only storage for photos. If that is what you want or need, you may want to explore 3rd party options such as Google Photos or Dropbox.

Another way that photos may be on iCloud (if you don’t have iCloud Photo Library turned on) is via a backup of an iOS device. The only thing you can do with a backup is use it to restore a device or set up a new device. The contents of backups are not viewable at iCloud.com and if you delete a photo from a device it will not be included in future backups and will be lost.

If you have synced it will be deleted from iCloud.

Upload to iCloud Drive (Use as many Folders as you want) or Use iCloud Shared Album it will remain

File types that you can use in Shared Albums

Shared Albums support these image formats:

• HEIF
• JPEG
• RAW*
• PNG
• GIF
• TIFF

Shared Albums also support special formats that you capture with your iPhone, like slo-mo, time-lapse, Live Photos, and Memory videos. When shared, photos taken with standard point-and-shoot cameras, SLR cameras, or iOS devices have up to 2048 pixels on the long edge. Panoramic photos can be up to 5400 pixels wide. You can share GIFs that are 100MB or smaller.

Shared Albums support these video file types and formats:

• HEVC
• MP4
• QuickTime 
• H.264
• MPEG-4 

Videos can be up to fifteen minutes in length and are delivered at up to 720p resolution.

* You can't upload RAW photos to Shared Albums on your Windows PC.

Shared Album storage limits

A Shared Album can hold up to 5000 photos and videos. If you reach your Shared Album limit, you need to delete some photos or videos before adding new ones. The photos and videos you share (and the comments or likes associated with those photos) stay in iCloud until you or the contributor delete them manually, or until you delete the Shared Album completely.

The photos and videos in your Shared Albums are kept in iCloud, but they don't count against your iCloud storage limit.

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Use Shared Albums in Photos - Apple Support

https://support.apple.com/en-us/HT202786

https://support.apple.com/en-us/HT204264