We hire PhoneGap developer to build an app. After the app finished, we found the app speed is very low and it hangs frequently. when we ask the freelance, he says our server is responsible for this issue.
However, I believe this is not correct because I use a same hosting company with other apps and websites without any problem plus we have only 3 users use this app currently.
Are there any tool can check the app performance? (something like Google PageSpeed for websites). If there are no testing tool like this, what should I do?
What platform(s) does the app target? You can use Google Chrome's Inspector tools to debug your android apps, which you can use to get lots of performance data, and Safari to debug iOS apps (not quite the same level of perf data).
For network stuff, you could run off a proxy to see how long network responses are taking if you can't debug any other way. I like Charles Web Debugging Proxy • HTTP Monitor / HTTP Proxy / HTTPS & SSL Proxy / Reverse Proxy (not affiliated in any way).
Furthermore, it might help to see what you mean by "very slow" and "hangs frequently". A video would be useful here just so we can get an idea of what you mean.