If I delete photos from my iPhone will they also be deleted from the cloud?

iCloud Photo Library is a syncing service. Any photo you delete from a device where iCloud Photo Library is turned on will also be deleted from iCloud and from any other device connected to that iCloud Photo Library. You can potentially reduce the storage space required on a device by turning on Optimize Storage. See: iCloud Photo Library - Apple Support

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.

I use iCloud Photo Library on my iPhone and on my Mac. On the Mac I also have Google Photos turned on. (in addition to local backup via Time Machine & Carbon Copy Cloner and offsite backup via Mozy).

Yes, as that's how iCloud works. It was designed like that, i.e. a synchronization system.

Curious, what do you use for your photos needs FoxFifth?

Thanks, appreciate it! 🙂

I should have also said that my photo library is small (2GB) by most standards. I try to avoid making any recommendations about cloud solutions if I know they involve 100GB etc libraries.