When your iPhone's storage fills up, emptying the trash can be one of the fastest and easiest ways to free up space. But the process is a little different than on a computer, as iOS doesn't have a single Trash folder where all deleted files end up.
Instead, individual apps have their own trash folders where deleted files are temporarily stored for a short time before being permanently erased. This can result in the apps' trash folders growing over time, taking up valuable storage space. And it's important to clear these trash folders periodically so you don't run out of space on your iPhone.
In the Mail app, for example, deleted emails and junk email will continuously take up memory in your Trash folder until it's cleared. To empty the Trash folder, open the Mail app and tap the email account you want to clear the Trash for. Then tap Trash, which will open the Trash interface. Scroll down and tap the Edit button, which will let you choose which emails to delete. If you have multiple email accounts, you'll need to repeat the process for each of them.
In addition to the Trash folder, there's also a "Recently Deleted" section in the Notes app where deleted notes are temporarily retained for 30 days before being permanently erased from your iPhone. You can also find the Trash and Junk folders in the Files app, where you'll need to select all the selected files to delete them permanently.