I assume you are using Fairphone OS 1.8.7 Kola Nut, which was released in mid 2015. This means that it hasn’t received any security updates for over 3 years. I don’t recommend installing a banking app on your FP1.
As for rooting: FP1 is rooted, which means that you have administration rights on your phone and can modify everything. It also means that potentially malware can gain root privileges and steal data from other apps (in this case your banking app). This is why banking apps usually don’t run on a rooted phone.
I myself don’t use any banking app on my FP1 and thus never have had the need for another app that hides root from a banking app. I think that there is a Xposed module called Root Cloak. However, as said before, I wouldn’t recommend it as there are security concerns.