The Time Capsule (two generations shown) was a hardware device that combined a wireless router with a built-in hard disk to offer wireless backup using Time Machine.

AirPort Time Capsule stores it all — up to 2TB or 3TB of data.Once it is setup on the network, it’s immediately available as a file server and Time Machine backup target. As a Time Machine target, it takes a snapshot of the entire system as an initial backup after which, only the files you’ve changed are backed up — automatically Follow our simple step by step guide to browse your Apple Time Capsule with your iPhone or iPad. These details apply to TimeCapsule and to AirportExtreme devices with attached USB hard drives - where 'TimeCapsule' is mentioned below, if you have an AirportExtreme, the same applies. The all-new elegant design and the support for 802.11ac Wi-Fi aside, the new Apple AirPort Time Capsule is very much the same as the previous generation. Yes, I know you can back up the iPhone to your computer and then back the computer up to Time Capsule. It would be better if the iOS device would back up directly to Time Capsule. This can be an alternative to people who would like to backup a large iOS device, but do not want to use iCloud.

Oct 28, 2016

May 13, 2016 AirPort Time Capsule as Time Machine, not router: How to Feb 21, 2020

Backing up iPhone using Time Capsule - Apple Community

AirPort Time Capsule is designed to partner seamlessly with Time Machine in OS X Leopard or later to protect your data. They work together smartly so that after the initial backup, only the files you’ve changed are backed up — automatically, wirelessly and in the background.