Which SQL query for first name, last name, phone number?

I would like to retrieve the user information such as first name, last name, phone number from Community Builder database tables.
I made a form with Balbooa Forms.
In it I can have fields automatically filled with a SQL query.

I understand the query to select a user by ID, but I would like to retrieve the data from the currently logged in user.

Who can help me with the correct SQL query?

Core CB fields and custom CB fields are all stored in the _comprofiler table. You'll find that information there. For core Joomla fields you'll find that information in _users. I cannot help you with custom coding, sorry. Suggest reviewing those tables carefully and trying queries in phpmyadmin.

Thank you for your response.
In comprofiler I see all the data of all users.
But I can't find a value there that indicates that it is the specific logged in user.

Suppose I want to display the first name of the logged in user in a form field.
Where could I find it?

Login status is entirely contained in Joomla's sessions. Those are stored in the _sessions table. If they have a row in that table matching their userid they're logged in.