Too many Photos

The trick is to come at it from the other side :)

Import photos from another library in Photos on Mac - Apple Support

Open the destination library and import to it, not export from the other. However, according to that document there is another problem for you:

as long as the library you want to import from doesn't have iCloud Photos turned on.

It might be worth considering PowerPhotos for the job, but read the documentation first.

https://www.fatcatsoftware.com/powerphotos/

https://www.fatcatsoftware.com/powerphotos/Docs/index.html

On the other hand, you could create the new Library (as you've done) and in Settings make the New Library the System Library. Then you can turn on iCloud in Settings in this New Library-- this will automatically disconnect your Old Library from iCloud. iCloud will go, "Hey, what happened?" and start re-populating your new System Library (the New Library) with all the pictures in iCloud Photos. After maybe a few days, the New Library will have everything in it, and you now have two libraries with all your pictures.

In the New Library you can command-delete all the pictures over a year old, and that that will sync iCloud Photos to do the same there and to your phone. So iCloud and your phone will have only recent pictures in them.

This will take a few days (if you have a large library), but it all happens automatically. Keep the computer on overnight, but with Photos in the background and with other apps up front. Photos doesn't like to do management stuff if it thinks that you're working in it.

And, whatever you do, back up your existing Library to an external hard drive first.

What version of Photos do you have?