How can I get more Storage on my phone?

There's no way to increase the storage on an iPhone — you´re stuck with what you bought! As kb 1951 suggested delete unused items, such as apps. You might also have a ton of photos which you can download to your computer via iTunes and then delete from your phone. Also go to Settings > General > iPhone storage and have a look at what's taking up unnecessary space. And have a look at your mails and Social media (WhatsApp, Twitter etc.). There's probably a lot you can delete there. Hope this helps! Ian.

@juan: there is also the option of transfering your photos/videos (assuming that they are the ones taking much of your space) to a cloud based service and accessing them via wifi/cellular data.

Depending on your phone, for older model like 5s/6/6s (at last for these I know it), there are available cases with expanded memory. Don't know if they still work in iOS 11, but check the web and see exactly if they are available for your phone/iOS mix.

The only way to get more storage is to delete unused items from the phone.

Yes, you´re absolutely right! I didn't suggest this because I personally don't use a cloud-based service (like iCloud Photo Library or Google Photos) for my photos/videos, and am very careful about suggesting something of which I have no personal experience! Ian.