I was recently volunteering at an event my church puts on every year called ServeFest. It's a neat event where instead of having church, we give to the community we're a part of by providing free clothes, school supplies, vaccinations, haircuts, family photos, food, bike repair, and other great things. It's often an event where people take a lot of photos, usually on their phones. During the event, one of my friends tried to take a video on her iPhone 6s Plus and got the message that she was out of storage. Since she had a 16GB iPhone, it wasn't that hard to do. iPhone 6s (plus) has a 12 megapixel camera and the ablity to shoot 4K video, which can take up a lot of storage very quickly. After looking in a couple places, there wasn't a whole lot we could do to remedy her situation. After realizing that this is a big issue, probably for a lot of people, I looked into the best ways to handle having an iPhone with low storage. Here are the options and suggestions I found to be the best way to go.
iCloud Photo Library & Optimize iPhone Storage
Apple's own iCloud has some options for photo management and storage saving, but to be honest, they're not as effective at saving space, and they're not free. iCloud comes with 5GB of storage for free, but this is shared with your emails, documents, contacts, iPhone backups, and other data. I don't know anyone who is doing iPhone backups and photos storage in iCloud that is able to stick with the free option. The lowest paid teir is 99 cents per month for 50GB of storage. This is a competative and good price for storage and should work for most people. The optimal settings for using iCloud to save local storage on your iPhone is to enable iCloud Photo Library in Settings > iCloud > Photos and have the option for Optimize iPhone Stoage selected. Doing this, I've got my whole photo library stored online which takes up about 26GB of my iCloud storage. Checking locally, the photo library takes up about 13GB on my iPhone even with it being "optimized." So about half of the total library is stored locally. If your photo library isn't that big, maybe you can get by with a 16GB iPhone, but my friend's iPhone wouldn't be able to store even my "optimized" library locally.
Delete Old Photos
One thing you could be doing is deleting your photos you don't need around anymore. I personally don't like to delete photos very much because I'm a digital hoarder, but if you don't mind doing some clean up every now and then, you could save a ton of space. If you've got a lot of photos you want to delete at once, you can tap the select button in the top right corner of the photos app when you're in the Moments view, then tap each photo you want to delete, then tap the trash can in the bottom right of the screen. Even quicker bulk selecting can be done by tapping the first photo of a group, then dragging left or right to select all the photos between the first and last photos touched. This even works when dragging up and down on mulitple rows, but you have to first drag left or right, then up or down.
One way to save space quickly is by deleting unneeded apps that take up a lot of space. The quickest way to do this is by checking in Settings > General > Storage & iCloud Usage > Manage Storage. This shows you a list of all the apps on your iPhone in order of most to least storage used. That way you can either delete the app, or go into it and delete documents or data it's got lying around. Some apps might take up a bucnh of storage even though they shouldn't; Snapchat on my friend's iPhone took up a whole gigabyte of storage for seemingly no reason. The easy fix was to delete and redownload to shave off almost 90% of that gigabyte down to about 120 megabytes.
Get A Bigger iPhone
I know this doesn't help those of you who already have a 16GB iPhone, and Apple doesn't even sell 16GB iPhones (except the iPhone SE) anymore since the release of the iPhone 7, but one of the best ways to remedy a phone with low storage is to upgrade to a bigger phone when you've got the chance. I think you'll fine the extra $100 to have been worth it when you realize the luxury afforded of never needing to delete your photos, manage your apps, or get annoying popups when you want to take a video.