Two separate businesses and separate bank accounts. I have a single cellphone I am using for both businesses.

Depending on how you answer you have 2 options.  A second all new square account or a Second location on your current account.

using one device will complicate it slightly as you will have to sign in and out of the account you want to use each time, which can lead to errors in forgetting to change the login.

Then you will want to open a second square account (It is free so no worries) that way money and taxes etc will be kept separate for accounting.