IPhone storage never has enough space?

Title says it all. I owned 600 photos, and placed a majority of them onto my computer, deleting them off my phone. There's about 200 now. Which is nothing compared to the storage space purchased from my phone company.
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I've also deleted apps I didn't use anymore, and cleared my email that had hundreds of spam stuff. But yet it's STILL full. I'm a photographer and editor, therefore I hold quite a bit of photos for my portfolio on my phone. Plus newly taken photos for future editing. I need more space to hold these work in progress photos and no matter what I do my storage is always full. Any methods or reasons why this is happening?
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I can't buy more storage so I don't need any comments mocking me. They'll just be deleted. As well as stupid answers that don't relate to the question.

The amount of space taken up by a photo image file will vary depending on the subject matter in the image, the compression ratio of the file format, and the resolution on the image.

Many modern phone cameras can take images with 15 to 20 million pixels. Before compression that can be over 50 MB for an image in 24 bit colour. Depending on subject matter and compression, this might come to over 10 MB per image. On that basis 600 photos would use 6GB. Videos take much more.

It is rarely necessary to carry so many images with you, and for safety you should be backing anything important on to two separate storage media. Your phone should not be the only place photos are stored.

I would suggest getting a Windows tablet PC that you can use to show your portfolio and to keep your first level backup, then do a proper backup when you return to base. For exhibiting your work, a larger screen can be a big advantage.

Also, I have a battery powered Toshiba 1 TB drive with an integrated Wi-Fi router. It is small enough to fit in my pocket, and I can transfer photos between the drive and my phone when I'm out in the countryside and away from normal power and network resources.

You can trying installing some cloud storage options. Subscribe to a few. One Drive and Google Photos gives you 5GB and 15GB respectively. Google Photos can be set to give you unlimited storage, if you don't mind the photos being compressed.