I’m trying to save all my apps to my iCloud so I can clear space on my phone, but I am unable to. How do I do this?

There is nothing as "copying" iPhone data to iCloud.

You may only sync iPhone to iCloud. That means if you delete anything on iPhone it will be deleted from iCloud too.

However you may optimise iPhone storage

If your iPhone XS has optimised storage enabled then it may have lower space. Know about it. With Optimize Storage, smaller, space-saving photos and videos are kept on your device while all of your original, full-resolution versions are stored in iCloud. And as long as you have enough space in iCloud, you can store as many photos and videos as you want.

Store your photos and videos in iCloud

Your photos and videos are stored on your device in their original, high-resolution version. This means that they use a lot of space on your iPhone, iPad, and iPod touch. With iCloud Photos, you can make more space available on your device and have your entire collection, everywhere you go.

Get started with iCloud Photos:

1. Tap Settings > [your name] > iCloud > Photos.
2. Turn on iCloud Photos.
3. Select Optimize iPhone Storage to save space on your device.
4. 

With Optimize Storage, smaller, space-saving photos and videos are kept on your device while all of your original, full-resolution versions are stored in iCloud. And as long as you have enough space in iCloud, you can store as many photos and videos as you want.

As far as Apps are concerned, noelle1222, you can choose to Enable Offloading of Unused Apps (a rather usual RECOMMENDATION under i[Device] Storage). This option can be found in Settings -> iTunes & App Store -> Offload Unused Apps.

"Automatically offload unused apps when you're low on storage. Your documents & data will be saved."

You can also go to any Apps, in the listing of Apps using i[Device] Storage, and choose to "Offload App": "This will free up storage used by the app, but keep its documents and data. Reinstalling the app will place back your data if the app is still available in the App Store." (emphasis added)