Uninstalling the app on mobile means that all your unsynced content is gone from your device, and there's no way to access it again for you.
We you use Collect without an account, we do not link any of your personal details to local use of the app. We believe you deserve privacy when you use our app, and if we don't need to save your details, we don't.
But I want to keep my files!
Don't worry, you can sign up for an account to keep your boards online. With a free account, your boards will sync to to the 5 GB limit, and will be available when you access Collect again. This article explains how you can create an account.
If you have more than 5 GB of content in Collect, you can subscribe to Collect Pro which allows you to sync up to 200 GB! Make sure that the sync is completed before deleting the app (look for the cloud icon on each board), we cannot save boards which haven't finished syncing.
But I just want to delete my files!
If you want to delete your content stored within the Collect, please ensure you also delete your boards manually by following the steps in this article. From here, you can delete your account from the Account tab on the mobile app.