You can free up space on an iPhone by deleting apps, photos, and videos. To free more space on your iPhone, clear Safari's cache and delete old messages. To see how much storage space is left, head to Settings > General > iPhone Storage.

When you’re low on storage, you can have iPhone automatically remove unused apps. Go to Settings > General > iPhone Storage. Tap Enable next to Offload Unused Apps. The unused apps move to iCloud Drive. You can find them in iCloud Drive in the Files app. You can also remove many apps manually, and redownload them if you change your mind.

You can do so by launching the 'Settings' app > tap on 'General' > select 'iPhone Storage > and enabling the option to 'Offload Unused Apps'. Once that's done, your phone should automatically delete unused applications when you're running out of storage space.