When a file is deleted, the space used on the disk is not reclaimed until the file is truly erased. The trash (recycle bin on Windows) is actually a hidden folder located in each hard drive. To completely delete the file, another step must be performed.
Cached Data: Sometimes, apps store temporary data or cache files on your phone's internal storage. Even if you delete files, these cached data may still occupy space. Clearing the cache of specific apps or using a cache cleaner app can help free up storage.
Check the Recently Deleted Folder
This means that deleted data still exists on your phone—and is synced to iCloud—for some time, despite you having deleted it. People commonly forget to clear this album out since the folder is buried far down in the Photos app.
Your free space might actually be occupied by your operating system, so you may need to uninstall more apps to make more room. Use a cleaner app to free up space on your Android after you've done what you can but are still unable to make room.
An Uncleared Cache
A cache can come in the form of hardware or software, and its function is to store data so that future requests for that data can be processed and provided in less time. But a cache can also harbor data that you no longer need, and therefore takes up storage space without you even realizing it.
Open your iPhone's Settings menu, tap General and go to iPhone Storage. You'll see a list of your apps along with how much space each app occupies and the last time you used it. Scroll through the list and try deleting apps that you haven't used in a long time. Get rid of apps you haven't used in a long time.
Photos and videos that are fewer than 30 days old may be retained on your device. They'll still be backed up in your Google Photos library. Important: Before you delete your photos, make sure that they're backed up. Learn how to back up photos.
Factory reset your iPhone.
Restoring your iPhone to its original settings is a big step, but it often clears space you can't delete in any other way. Consider it as a last resort solution.
Clearing data will not delete the app updates. When you open the app after clearing its data, you will see the latest version that was previously installed on your phone. Similarly, clearing data will not delete any of your accounts. You will only be logged out from most of the apps.
Clearing your Android app cache can help fix speed issues and free up storage space. If you need more storage, clear the cache of the apps that take up the most space. Clearing your app cache every few months will help streamline your phone and keep it from getting too full.
Either you are installing more apps, or the apps you have are writing data/files to the internal storage over time which is filling it up. I think, it's better use Link2SD app to move apps to SD card 2nd partition. It more effective than ordinary apps moving method.
Knowing how to clear your web history can help you protect your privacy online. Clearing search history and browsing history frees up space on your device and helps hide your activity.
And when a phone's storage is almost full, it will automatically remove all backed-up photos and videos. If you don't want to do that, you can manually clear out your downloads by going through your download directory, Fisco says.
It's not bad to clear your cached data now and then. Some refer to this data as “junk files,” meaning it just sits and piles up on your device. Clearing the cache helps keep things clean, but don't rely on it as a solid method for making new space.
Clearing your cache removes stored data that helps websites and apps open faster, while offloading temporarily uninstalls an app without deleting any of the documents and data associated with that app. Both methods can help speed up iPhones that are slowed down by low storage.
When you tap Erase All Content and Settings, it completely erases your device, including any credit or debit cards you added for Apple Pay and any photos, contacts, music, or apps. It will also turn off iCloud, iMessage, FaceTime, Game Center, and other services.
Check the Sent folder or any other folder you think may contain emails you can delete. Regular emails do not take up a lot of space. To free up the most space in Gmail, you can delete emails that contain attachments, such as documents, photos, songs, etc.