salesforce1 app and salesforce web app on mobile look to be so similar to each other. Is salesforce1 app an iphone app used web view to embedded web app or phonegap app?
Neither, but you're on the right track. It uses a framework called Aura. It's like phonegap but has a different API and set of features. This is documented here with links to official resources.
@sfdcsfox is correct about the framework Aura. There is a slight difference between Salesforce in the mobile browser and the installed Salesforce1 app. They could be using different "browser" versions. To be clear, when I log in to Salesforce using my mobile browser it gives me the Salesforce1 view, but I could also just navigate directly to
https://<instance>.salesforce.com/one/one.app in my mobile web browser.
The first image is from the installed Salesforce1 app. The second is from the mobile browser (one/one.app). You can see the installed Salesforce1 app has Chrome 30 whereas the mobile browser (one/one.app) is Chrome 34.