An iPhone 6 would certainly be a viable option for a work phone, depending on what kind of work you're doing. If you merely require basic functions like calls, emails, and maybe some light app usage, it will serve just fine. However, if you're seeking something more intensive like modern productivity or graphic-heavy applications, the iPhone 6 might fall behind due to outdated hardware. Also, if you're considering video conferencing, newer phones have better camera quality.
Remember to purge it of any personal data and ensure it's updated to the most recent operating system it can handle. This is to stay relevant with security measures and app compatibility. Battery life can also be an issue with older phones, so keep that in mind too.
Ultimately, it's down to your requirements. Sure, it’s not the latest and greatest, but as long as it gets the job done for your works, that's all you need.