Can my employer require me to install an app on my personal phone?

It will depend on what's in your contract. It may require you to bring your own devices. They may have to provide you with the correct equipment or have a tech fund set aside.

I imagine the law would be that as long as you can do the work safely, it's not putting you under minimum wage, the company wouldn't own it, and you're not required to buy your company's software, then it's up to you to agree it with your boss. It would presumably then be treated like any other work expense.

Of course, it would be pretty stupid if your job tried to get you to buy all of the software and hardware you needed. What are they going to do if you just don't buy it? They are de facto obliged to get you the right equipment.

In this case though, your boss might just think you're being a bit of a turd. Assuming the app is simple and not intrusive, and seeing as you likely have a perfectly good Smartphone that could handle the task without issue.

It's not like they'd have to buy you a phone. They could just get an office tablet, lend you their phone, or get you to install the app on your PC. Or take you off the client and find someone else who will do it.

/r/AskUK Thread