iPhones are always running out of space, and will probably continue to do so forever. Now matter how much space you've got, you're bound to find ways to fill it.
Sadly it isn't practical, unless you're an extremely proficient DIYer, to open up an iPhone and upgrade its flash storage modules, which are soldered directly on to the logic boards. Whatever storage allocation it came with at purchase, that's what you're stuck with. (Which is why we always recommend buyers to go a little higher than they think is necessary.)
But there are some other ways to approach this issue. In this article we explain how to increase storage on an iPhone. Read next: iPhone buying guide 2017
Plug-in storage devices
iPhones don't come with an SD card slot (a universal connector which enables owners of many Android handsets to expand their storage very cheaply and easily). Instead they come with the proprietary Lightning data port, which replaced the 30-pin dock in 2012.
This can be a pain, but fortunately Apple's industry clout is sufficient that accessory makers have made plenty of removable storage accessories that are compatible with Lightning.
Bear in mind that this isn't a perfect solution.
You can either have the device plugged in all the time, in which case you lose the sleek looks and to some extent the portability of your iPhone. Or you plug it in as and when you require whatever is stored on the drive, but this means having to carry around an extra accessory, and the potential that you won't have it with you at the exact moment you need it.
We recommend a bunch of plug-in storage accessories in our article Best external storage drives for iPhone, but here are a few that we'd particularly pick out:
Storage-expanding iPhone cases
If you want a slimline always-on option, consider a storage-expanding phone case. This fit over the iPhone and connect via its Lightning port. You may still be able to charge your iPhone without removing the case - many feature a charging port on the exterior - but you should check.
SanDisk does something similar (with more storage - 32GB, 64GB or 128GB - but the battery comes separately) for iPhone 6 and 6 Plus: iExpand Memory Case. That has a headphone port opening but we'd have thought that otherwise it would fit the iPhone 7 - check with the company if you're interested.
We rather like the design of the PKparis K'ablekey (available from Amazon for £58), which is done in brushed aluminium and has built-in magnets that keep the two semi-circle halves stuck together for easy transportation. When you want to use the cable, simply pull off the orange rubber ends and pull the two sections apart.
Leef does some nice plug-in storage accessories too. The Leef iBridge 3 supports USB 3.1 for transferring files to PC or Mac, and goes all the way up to 256GB. And the Leef iAccess iOS Micro SD is another possibility, effectively giving you an SD Card slot.
Wireless hard drives
This is a rather more elegant solution. If you've got files you want to be accessible on your iPhone but no space for them, store them on a standalone drive you can access over Wi-Fi.
As before we've got a larger selection in a separate article, but here are some worth considering.
LaCie's Fuel 1TB Wireless has a USB 3.0 port, so can turn its hand to service as a conventional hard drive with your Mac, but also has built-in Wi-Fi. Claimed battery life is up to 10 hours. It costs £134.95 from Apple's website.
If you don't need all that much storage try SanDisk's Connect Wireless USB 2.0 Flash Drive, which comes with 32GB. It costs £39.99 and can be had from John Lewis.
This is the top-end choice for expandable storage.
Apple's AirPort Time Capsule is the obvious choice: you can get 2TB for £299, or 3TB for £399, and either model can be used to set up a Wi-Fi network and connected to your iOS devices. But the file-management features between the two devices won't work brilliantly - it's a bit fiddly - and you'll want to install a third-party app such as FileBrowser to make things easier.
We'd recommend instead that you go for something like the WD My Cloud. WD offers decent iOS apps which make it easy to use advanced features like remote access and share files with friends and family. You can go up as high as 16TB, or buy the frame on its own and add your own drives.
Store files in the cloud
The solutions above all involve buying additional hardware so you can store some of your files off the iPhone. But we can take this strategy one step further.
By storing files in the cloud we outsource the storage to other people's servers, while retaining access to them whenever we're able to get online. Some of Apple's cloud services can be helpful in this regard, but others cause as many problems as they solve.
Music is one of the big four filetypes (along with apps, photos and videos) that tend to clog up iPhones. But you don't have to have every iTunes track you could ever possibly need to listen to on your iPhone.
Sign up for iTunes Match (which starts at £21.99 a year) and every track you own will available via the cloud, enabling you to delete it from your iPhone and free up some space. Here's how to set up iTunes Match. You can sign up here.
iCloud Photo Library
Let's talk photos (and videos) next.
iCloud Photo Library lets you automatically upload and store your entire library in iCloud, which might sound like the solution to storage space problems. But the problem with Photo Library is that it stores all your images taken on all your devices on your iPhone. These are stored in a reduced file size, but they still take up space. Read next: How to back up your Apple photo library
Photo Stream is a cloud-based service but in terms of storage requirements it can be as much of a double-edged sword as iCloud Photo Library. With it switched on you'll find that you can see photos you've taken on your iPhone or iPad, as well as those you have uploaded to your Mac from your camera. These images aren't full-res, but are still likely to take up a lot of space on your iPhone.
From a pure storage point of view it's probably best to go to Settings > Photos & Camera and untick My Photo Stream. (You can always turn it back on again after the storage issue has passed.)
However, you might decide that 1GB of Photo Stream images is worth the sacrifice for being able to easily back up the photos you take on your iPhone. Read more: iCloud Photo Library or My Photo Stream: Which is better?
Third-party cloud services
For many filetypes the best option may be to go off reservation and sign up with a third party.
There are plenty of options for uploading files from your iPhone to cloud-based services, such as Dropbox, Google Drive and Microsoft's OneDrive. These all provide free options with varying amounts of online storage - Google lets you have 15GB, for example.
Tips to free up space
If you're not interested in expanding the available space using external storage devices or cloud services, we'll simply have to do some careful pruning.
Find out which apps are taking up most space
Go to Settings > General > Storage & iCloud Usage, then tap Manage Storage in the first section. Your apps will be listed in order of size. Be brutal.
Delete old messages
By default Messages keeps texts and iMessages forever, but you can change this so it ditches them after 30 days or a year. Go to Settings > Messages > Message History > Keep Messages, select a time parameter, then click Delete.
Delete non-HDR photos
Your phone can use High Dynamic Range to capture better photos. On older iPhones this mode can be a bit hit and miss because of the slower camera, so it's a good idea to keep the normal photo just in case. But on newer iPhones HDR works well enough that you can safely manage without.
Go to Settings > Photos & Camera and deselect Keep Normal Photo.
We've got lots more of this sort of thing here: How to free space on an iPhone