I used to have a second phone. But it was difficult to hide, and have in the right place to access. And explain, if found. I was constantly worried about it.
But, I now have a second sim in my regular phone, it can be turned off, stopping texts / calls coming through when you don't want them. It's far easier for me, but I am methodical and OTT about cleaning all evidence from my phone after a punt. Nothing kept, names,numbers, texts, nothing.
Android also has a "secret folder", which can be renamed, password protected, and a logo chosen. Where you can activate a second WhatsApp account, snapchat, whatever you need. I install, use as required, and uninstall the apps again everytime. As I said, OTT... but has worked for me for years.