Hello,my mobile shows storage full, others are 40gb why?

You must have iOS 13.7 or higher. Now the question is what is "Other" storage. Read on...

• Other: Non-removable mobile assets, like Siri voices, fonts, dictionaries, non-removable logs and caches, Spotlight index, and system data, such as Keychain and CloudKit Database. Cached files can't be deleted by the system.
• System: Space taken by the operating system. This can vary based on your device and model.

About cached files in "Other"

Finder and iTunes categorize cached music, videos, and photos as Other instead of actual songs, videos, or photos. Cached files are created when you stream or view content like music, videos, and photos. When you stream music or video, that content is stored as cached files on your device so you can quickly access it again.

Your device automatically removes cached files and temporary files when your device needs more space.

If storage on your device differs from what you see in Finder or iTunes

Since Finder and iTunes categorize cached files as Other, reported usage for Music or Videos might differ. To view usage on your device, go to Settings > General > [Device] Storage.

If you want to delete the cached files from your device

Your device automatically deletes cached files and temporary files when it needs more space. You don't need to delete them yourself.

In short --> IGNORE, if you are not convinced, Restart the device. You will see that Others Storage will reduce but total storage will remain more or less the same.

Watch the demo in the GIF below made on my iPhone 6 iOS 12.4.7

In short --> IGNORE, if you are not convinced, Restart the device. You will see that Others Storage will reduce but total storage will remain more or less the same

Keeping in mind that the “other” storage category is mostly filled with cache and system files created by Safari, the Mail app, other apps and iOS/iPadOS itself, that space is automatically managed by the operating system and you can’t interact with it.

That said, update your device to iOS/iPadOS 13.6.1 or later, as per this support article: Clear Other storage on your iPhone or iPad - Apple Support

If you already updated your device to 13.6.1 or later to no avail, some benefits to reduce that space can be also obtained creating a full backup of your device, then restoring it to factory settings and, in the end, setting it up as new, as per these instructions: Restore your iPhone, iPad, or iPod to factory settings – Apple Support

When done, restore data from your previously made backup, then restart your device and check your device storage again.

If the issue persists, contact Apple Support directly, using this link: Get Support

Regards

Giulio