Hi
according to the Atlassian page “https://developer.atlassian.com/platform/forge/storage”, you can only access your data from your own app. The app storage is separated per app, so that it is not possible to access your app’s data by other forge apps due to security aspects. Therefore, I doubt that you will be able to find a way from outside the forge environment to access that data!
Maybe, a solution is to implement a web trigger within your forge app: this can be called from a php application and you would read the stored data and pass it back or visa versa.