For simple geotagging, any device that can reliably record a GPX track can work, but the easiest workflow depends on how accurate and hands-off you want it to be.

A phone can generate GPX logs, but battery life can be a real limitation on long walks. A dedicated GPS logger is often a better fit because it’s designed to record continuously for longer.

Several answers suggest that post-processing by matching timestamps works, but it can become tedious or error-prone if you need precise location data. If exact correlation matters, a device made specifically for camera geotagging is the better option.

One example mentioned is the JOBO photoGPS, which sits on the hot shoe and records location when you shoot, making later matching easier. Another budget-style option mentioned is an i-gotU GPS logger, which records tracks and can be converted to GPX for geotagging later.

So: if convenience and accuracy matter most, look for a camera-oriented geotagging device/logger. If cost matters more and you’re okay syncing timestamps afterward, a standalone GPS logger is a practical choice over using your phone.