Should I user Paypal on the server side or client side for a Phonegap App?
The Cordova-Plugin is built on top of PayPal Mobile SDK libraries, which provides a native in-app payment for your integration.
Literally you would be able to implement your complete payment flow with mobile platform SDK only (skip the payment-verify step on the server side), but that will necessarily depend on what your use cases are.
Here're the recommended solutions that will need some work on both platforms
The payment can be either (1) an immediate payment which your servers should subsequently verify, or (2) an authorization for a payment which your servers must subsequently capture, or (3) a payment for an order which your servers must subsequently authorize and capture
You may want to check here for some instructions on how the server side works for a mobile payment
For the record, the AngellEYE PHP library is for PayPal classic APIs and is irrelevant to this topic. Mobile payments are using REST apis and you may refer to the REST API PHP SDK for server-end implementations