what you can do is the in app browser to connect to a php driven page online and there do your paypal stuff.
http://docs.phonegap.com/en/2.3.0/cordova_inappbrowser_inappbrowser.md.html
function onDeviceReady() {
var ref = window.open('http://apache.org', '_blank', 'location=yes');
ref.addEventListener('loadstart', function() { alert('start: ' + event.url); });
ref.addEventListener('loadstop', function() { alert('stop: ' + event.url); });
ref.addEventListener('exit', function() { alert(event.type); });
}
Remember to white list the url that you will be using within phonegap else you will not to be able to make a connection.
On the php side write your own restfull api to handle the processing of the payments try to minimize the data sent to and from the api also try to use a secure connection if possible.
paypal examples can be found here: https://www.x.com/developers/paypal/documentation-tools/paypal-code-samples
its a solution but i do advise to use plugins for every platform, with those you can better guarantee safety, less bugs and less development time.