An observation: You are proposing to store Personally Identifiable Information in your system. If you store bank account details, an intruder into your system will be able to commit identity theft and bank fraud against the persons whose information is recorded. This is very dangerous. If I may speak as someone who's both an ordained pastor and a computer programmer, I urge you not to do this. It's simply not fair to your church's members to put them at risk this way. Emails, names, addresses? OK. That's the same stuff that's in your published directory. But be careful with names, genders, and ages of children.
At any rate, get the approval of your church's leadership for this project. You don't want sole responsibility for this.
I appreciate your attempt to keep personal information invisible to people among your staff and volunteers who don't need to know it. There's something in church work somewhere about avoiding temptation :-), and you're helping that. Good.
But: your most dangerous threat is not your staff and volunteers who can see your phpMyadmin pages. It is cybercriminals. If somebody cracks your system, they probably will crack your "control panel" -- your web application. If they do that, it doesn't matter whether you've encrypted those bank account numbers. For your web application to use that data it will need the key to decrypt that data. Cybercriminals know how to find that stuff. (See Matthew 10:16. Seriously.)
Set up multiple MySQL accounts, preferably one for each different person who will access your data base. Use phpMyadmin's user management page to do this. https://docs.phpmyadmin.net/en/latest/privileges.html
Then grant each user access to the databases and tables she's allowed to see. To prevent a user from seeing a table, don't grant her the SELECT privilege on that table.
You can do this with ordinary SQL too. It looks something like this:
CREATE USER 'JackTheTeacher'@'*' IDENTIFIED BY 'secret-password';
GRANT SHOW DATABASES ON *.* TO 'JackTheTeacher'@'*';
GRANT INSERT, UPDATE, DELETE ON `mydb`.`students` TO 'JackTheTeacher'@'*';
CREATE USER 'SallyTreasurer'@'*' IDENTIFIED BY 'another-secret-password';
GRANT SHOW DATABASES ON *.* TO 'SallyTreasurer'@'*';
GRANT INSERT, UPDATE, DELETE ON `mydb`.`pledges` TO 'SallyTreasurer'@'*';
GRANT INSERT, UPDATE, DELETE ON `mydb`.`donations` TO 'SallyTreasurer'@'*';
FLUSH PRIVILEGES;
This example grants Jack the right to manipulate the students table when he's using phpMyAdmin. It also grants Sally access to the pledges and donations tables. These are just examples to show you how to use fine-grained GRANT operations.
You can also ecrypt the contents of certain columns. But in that direction lies a false sense of security, because your web app needs the key to decrypt columns it uses, and your web app is probably the easiest route to crack your system.
