Created stack on iPad - how to sync it with iphone

I just starting looking at stacks tonight after installing iPadOS 15 (no problems to report on upgrade - yet). Looked through new features and decided to try the stacks feature - haven’t tried it on my iphone yet. Created a nice stack of apps that I think will server me wonderfully.

Background:

• stack created on ipad
• iphone iOS 15, iPad iPadOS 15
• same applications installed on both iphone and ipad

Question:

• how do I sync a stack between the two devices?

Thanks for any and all input….

Richard