Your Phonegap / Cordova app needs more persistent cookie based sessions.
<script src="cordova-cookie-jar/cordova-cookie-jar.js"><script>
<script>
// ... somewhere after cookies have been created
plugins.cookieJar.storeCookiesForDomain("your-domain.com");
// ... somewhere before you wish those cookies didn't disappear
plugins.cookieJar.restoreCookiesForDomain("your-domain.com");
// ... somewhere after those cookies are no good anymore
plugins.cookieJar.emptyCookiesForDomain("your-domain.com");
</script>