PhoneGap apps are more like hybrid apps. PhoneGap apps are not truly native: They use web views (not native UI frameworks) for layout rendering. PhoneGap apps are not purely web-based either: Unlike just web apps, they have access to native device APIs and are packaged as apps for distribution. PhoneGap is not the only cross-platform mobile development framework for creating hybrid apps like above, but it is arguably one of the most popular and most used cross-platform mobile dev frameworks in the world today.
The cross-platform mobile app development landscape has a number of players: PhoneGap, Titanium, RhoMobile, Sencha, etc. Though all of these share the same goal (cross-platform mobile development), there are differences in the manner in which each goes about achieving this goal. Depending on the context, you may have a narrower consideration set of cross-platform mobile dev frameworks and one of these may be the clear winner.
Companies like Mindfire Solutions provide expert cross-platform app development services using PhoneGap, Titanium, RhoMobile, etc. The dedicated PhoneGap, Titanium, and RhoMobile teams at Mindfire have a strong track record of developing powerful and engaging cross-platform mobile apps for global clients across diverse industry domains.