Practically, don't built your app that way. Apple, for one, frowns upon apps that are equivalent to simple wrappers around external web sites. Furthermore, your app must also be able to detect network connectivity issues, and without any local code, you can't do that (another common cause for rejection by Apple). You're also vulnerable to a host of security issues, not least of which would be a MITM attack that essentially replaces your entire app on the user's device -- and the user would have no defense against it.
Furthermore, by hosting on a server you don't fully control that is also shared with others puts your users at an even greater security risk. Should that server be compromised, your app could suddenly be serving a malicious version of your app. I don't trust a free host to properly manage the security of their servers, so the risk is too great, IMO. My suggestion: get a paid VPS with a SLA from a trusted provider. I use Digital Ocean and find them quite good, but there are plenty of other options out there as well. (You still don't fully control the environment your server is running in, but it's better than a shared server from a free web service.)
PhoneGap apps are typically built in the client-server pattern -- the client has most of the UI, and makes XHR (AJAX) calls to a web service (on a server somewhere) to get dynamic data. The client then renders the response. You still have security worries to be concerned about, but you can have local code that attempts to mitigate the issue and provide some sort of defense. Your local code can also inform the user about any network connectivity issues, and could even fall back to cached data if no network is available.
If you need to update the code outside the app store process, consider a code push solution like CodePush (no affiliation), Hydration (PGB), etc.