Do all phones have a QR scanner?

Virtually all phones from the last several years scan QR codes with the built-in camera app — no separate scanner app needed. iPhones have done it natively since iOS 11 (2017), and Android has had it built into the camera or Google Lens since roughly Android 9. Just point the camera; the link banner appears.

The exceptions worth knowing if you're printing codes for the public: very old devices need a scanner app, some budget Android cameras hide scanning behind Google Lens, and feature phones can't scan at all. That's why good practice is printing a short URL under the code — it costs nothing and covers everyone.

For businesses, the practical answer: your customers can almost certainly scan; whether they will depends on the code being big enough and the destination being worth it.