You will log in through facebook or Google when you make the purchase. The purchase is then tied to that account and the app can be downloaded on a different phone. This is the case with 99% of apps and tweaks.
However, there are a few apps that are tied to the phone number or hardware rather than the account. But in most of those cases, you can transfer the purchase to the new phone by contacting the developer.
It's impossible. Because, when we purchase any application from the store or Cydia, there is one specific account we need to use. So that application which we have purchased by using that particular account, that we can't transfer or install again to any other iPhone without an access of that account.