My 3 year old IPhone SE claims that it is full, but I don't have much on it? Details?

Over half of the storage is being taken up by "other." I cleared out my safari cache, and I don't have a reading list. I have 35 apps including the ones that come with the phone. I've off loaded 12 of them. I have like 5 pictures. I automatically delete texts after a month. I only have 55 contacts. E-mail and What's App are the 2 things that I can't clear out, but What's App only takes up 1.26 GB, and my e-mail only takes up 557.9 MB

Added (1). How do I get rid of the other? If I reset to factory settings, do I lose my apps, contacts, texts, e-mail, etc?

There's a lot of information taken up by system files and images people text, e-mail cache, what's app cache etc. You reset the phone and you will lose it. Unfortunately those 16gb phones all end up like this and Apple knew they would when they sold it. I tried to warn my friends and family, but some are stubborn and need to learn things the hard way. It's simply not enough space for any iPhone to function normally unless you constantly delete everything and install nothing.

It is likely other app's cache memory. Check that. You unfortunately can't clear them out via some app (as far as I'm aware) but in some cases it would simply be a matter of uninstalling & reinstalling it. Instagram & Facebook would be 2 examples of apps that usually accumulate a lot of cache memory over time. You would't lose anything since their data is stored elsewhere. Would simply be a matter of signing back in once it is downloaded. Could check back & again & verify the size dropped.

If you factory reset it, yes you would lose apps (though of course they can be reinstalled), contacts can also be synced back, texts (if backed up prior) & email would be downloaded once signed back in. It would help the storage situation but that's an extreme way of going about it.

Go into your settings and it shows you waht takes up the most space on your phone. Video can be big and should always be offloaded. Check to see what takes up the most in your settings.