Files Go is the new Google-made app that checks storage and frees up more space by identifying and deleting old files. Best of all, it takes up a relatively small amount of space on your device with no extras that can affect a phone's performance. The app is free for Android.
AMC Cleaner is another free and easy-to-use Android tool. It does deep scans revealing the big files occupying the most phone space. Things like old undeleted messages in social apps, unknown files and photos. Music and videos too, even more.
iPhone users have the Magic Phone Cleaner app featuring a simple interface to free up space. It evaluates available storage and identifies large photos and video files. It gives you the option to decide if you want to keep or delete them. The app is free for iOS.